Fix rates, acc and gyro coordinate frame in mavlink

All of them should be in frd.
Get rid of fluToFrd function - there is no big need for it.

.editorconfig

@@ -0,0 +1,15 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+[*.{ino,cpp,c,h,hpp,sdf,world,json}]
+charset = utf-8
+indent_style = tab
+tab_width = 4
+trim_trailing_whitespace = true
+
+[{*.yml,*.yaml,CMakeLists.txt}]
+indent_style = space
+indent_size = 2

.gitattributes

@@ -0,0 +1,2 @@
+# https://github.com/github-linguist/linguist/blob/master/docs/overrides.md
+*.h linguist-language=C++

.github/workflows/build.yml

@@ -0,0 +1,83 @@
+name: Build
+
+on:
+  push:
+    branches: [ '*' ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build_linux:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Arduino CLI
+      run: curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=/usr/local/bin sh
+    - name: Build firmware
+      run: make
+    - name: Build firmware without Wi-Fi
+      run: sed -i 's/^#define WIFI_ENABLED 1$/#define WIFI_ENABLED 0/' flix/flix.ino && make
+    - name: Check c_cpp_properties.json
+      run: tools/check_c_cpp_properties.py
+
+  build_macos:
+    runs-on: macos-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Arduino CLI
+      run: brew install arduino-cli
+    - name: Build firmware
+      run: make
+    - name: Check c_cpp_properties.json
+      run: tools/check_c_cpp_properties.py
+
+  build_windows:
+    runs-on: windows-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Arduino CLI
+      run: choco install arduino-cli
+    - name: Install Make
+      run: choco install make
+    - name: Build firmware
+      run: make
+    - name: Check c_cpp_properties.json
+      run: python3 tools/check_c_cpp_properties.py
+
+  build_simulator:
+    runs-on: ubuntu-22.04
+    steps:
+    - name: Install Arduino CLI
+      uses: arduino/setup-arduino-cli@v1.1.1
+    - uses: actions/checkout@v4
+    - name: Install Gazebo
+      run: curl -sSL http://get.gazebosim.org | sh
+    - name: Install SDL2
+      run: sudo apt-get install libsdl2-dev
+    - name: Build simulator
+      run: make build_simulator
+    - uses: actions/upload-artifact@v4
+      with:
+        name: gazebo-plugin-binary
+        path: gazebo/build/*.so
+        retention-days: 1
+
+#  build_simulator_macos:
+#    runs-on: macos-latest
+#    steps:
+#    - name: Install Arduino CLI
+#      run: brew install arduino-cli
+#    - uses: actions/checkout@v4
+#    - name: Clean up python binaries # Workaround for https://github.com/actions/setup-python/issues/577
+#      run: |
+#        rm -f /usr/local/bin/2to3*
+#        rm -f /usr/local/bin/idle3*
+#        rm -f /usr/local/bin/pydoc3*
+#        rm -f /usr/local/bin/python3*
+#        rm -f /usr/local/bin/python3*-config
+#    - name: Install Gazebo
+#      run: brew update && brew tap osrf/simulation && brew install gazebo11
+#    - name: Install SDL2
+#      run: brew install sdl2
+#    - name: Build simulator
+#      run: make build_simulator

.github/workflows/tools.yml

@@ -0,0 +1,33 @@
+name: Build tools
+
+on:
+  push:
+    branches: [ '*' ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  csv_to_ulog:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build csv_to_ulog
+      run: cd tools/csv_to_ulog && mkdir build && cd build && cmake .. && make
+    - name: Test csv_to_ulog
+      run: |
+        cd tools/csv_to_ulog/build
+        echo -e "t,x,y,z\n0,1,2,3\n1,4,5,6" > log.csv
+        ./csv_to_ulog log.csv
+        test $(stat -c %s log.ulg) -eq 196
+  python_tools:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Python dependencies
+      run: pip install -r tools/requirements.txt
+    - name: Test csv_to_mcap tool
+      run: |
+        cd tools
+        echo -e "t,x,y,z\n0,1,2,3\n1,4,5,6" > log.csv
+        ./csv_to_mcap.py log.csv
+        test $(stat -c %s log.mcap) -eq 883

.gitignore

@@ -0,0 +1,12 @@
+*.hex
+*.elf
+build/
+tools/log/
+.dependencies
+.vscode/*
+!.vscode/settings.json
+!.vscode/c_cpp_properties.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+!.vscode/intellisense.h

.vscode/c_cpp_properties.json

@@ -0,0 +1,144 @@
+{
+	"configurations": [
+		{
+			"name": "Linux",
+			"includePath": [
+				"${workspaceFolder}/flix",
+				"${workspaceFolder}/gazebo",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.2.0/cores/esp32",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.2.0/libraries/**",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.2.0/variants/d1_mini32",
+				"~/.arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.4-2f7dcd86-v1/esp32/**",
+				"~/.arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.4-2f7dcd86-v1/esp32/dio_qspi/include",
+				"~/Arduino/libraries/**",
+				"/usr/include/**"
+			],
+			"forcedInclude": [
+				"${workspaceFolder}/.vscode/intellisense.h",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.2.0/cores/esp32/Arduino.h",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.2.0/variants/d1_mini32/pins_arduino.h",
+				"${workspaceFolder}/flix/cli.ino",
+				"${workspaceFolder}/flix/control.ino",
+				"${workspaceFolder}/flix/estimate.ino",
+				"${workspaceFolder}/flix/flix.ino",
+				"${workspaceFolder}/flix/imu.ino",
+				"${workspaceFolder}/flix/led.ino",
+				"${workspaceFolder}/flix/log.ino",
+				"${workspaceFolder}/flix/mavlink.ino",
+				"${workspaceFolder}/flix/motors.ino",
+				"${workspaceFolder}/flix/rc.ino",
+				"${workspaceFolder}/flix/time.ino",
+				"${workspaceFolder}/flix/wifi.ino"
+			],
+			"compilerPath": "~/.arduino15/packages/esp32/tools/esp-x32/2411/bin/xtensa-esp32-elf-g++",
+			"cStandard": "c11",
+			"cppStandard": "c++17",
+			"defines": [
+				"F_CPU=240000000L",
+				"ARDUINO=10607",
+				"ARDUINO_D1_MINI32",
+				"ARDUINO_ARCH_ESP32",
+				"ARDUINO_BOARD=D1_MINI32",
+				"ARDUINO_VARIANT=d1_mini32",
+				"ARDUINO_PARTITION_default",
+				"ESP32",
+				"CORE_DEBUG_LEVEL=0",
+				"ARDUINO_USB_CDC_ON_BOOT="
+			]
+		},
+		{
+			"name": "Mac",
+			"includePath": [
+				"${workspaceFolder}/flix",
+				// "${workspaceFolder}/gazebo",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.2.0/cores/esp32",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.2.0/libraries/**",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.2.0/variants/d1_mini32",
+				"~/Library/Arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.4-2f7dcd86-v1/esp32/include/**",
+				"~/Library/Arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.4-2f7dcd86-v1/esp32/dio_qspi/include",
+				"~/Documents/Arduino/libraries/**",
+				"/opt/homebrew/include/**"
+			],
+			"forcedInclude": [
+				"${workspaceFolder}/.vscode/intellisense.h",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.2.0/cores/esp32/Arduino.h",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.2.0/variants/d1_mini32/pins_arduino.h",
+				"${workspaceFolder}/flix/flix.ino",
+				"${workspaceFolder}/flix/cli.ino",
+				"${workspaceFolder}/flix/control.ino",
+				"${workspaceFolder}/flix/estimate.ino",
+				"${workspaceFolder}/flix/imu.ino",
+				"${workspaceFolder}/flix/led.ino",
+				"${workspaceFolder}/flix/log.ino",
+				"${workspaceFolder}/flix/mavlink.ino",
+				"${workspaceFolder}/flix/motors.ino",
+				"${workspaceFolder}/flix/rc.ino",
+				"${workspaceFolder}/flix/time.ino",
+				"${workspaceFolder}/flix/wifi.ino"
+			],
+			"compilerPath": "~/Library/Arduino15/packages/esp32/tools/esp-x32/2411/bin/xtensa-esp32-elf-g++",
+			"cStandard": "c11",
+			"cppStandard": "c++17",
+			"defines": [
+				"F_CPU=240000000L",
+				"ARDUINO=10607",
+				"ARDUINO_D1_MINI32",
+				"ARDUINO_ARCH_ESP32",
+				"ARDUINO_BOARD=D1_MINI32",
+				"ARDUINO_VARIANT=d1_mini32",
+				"ARDUINO_PARTITION_default",
+				"ARDUINO_FQBN=esp32:esp32:d1_mini32",
+				"ESP32",
+				"CORE_DEBUG_LEVEL=0",
+				"ARDUINO_USB_CDC_ON_BOOT="
+			]
+		},
+		{
+			"name": "Win32",
+			"includePath": [
+				"${workspaceFolder}/flix",
+				"${workspaceFolder}/gazebo",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.2.0/cores/esp32",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.2.0/libraries/**",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.2.0/variants/d1_mini32",
+				"~/AppData/Local/Arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.4-2f7dcd86-v1/esp32/**",
+				"~/AppData/Local/Arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.4-2f7dcd86-v1/esp32/dio_qspi/include",
+				"~/Documents/Arduino/libraries/**"
+			],
+			"forcedInclude": [
+				"${workspaceFolder}/.vscode/intellisense.h",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.2.0/cores/esp32/Arduino.h",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.2.0/variants/d1_mini32/pins_arduino.h",
+				"${workspaceFolder}/flix/cli.ino",
+				"${workspaceFolder}/flix/control.ino",
+				"${workspaceFolder}/flix/estimate.ino",
+				"${workspaceFolder}/flix/flix.ino",
+				"${workspaceFolder}/flix/imu.ino",
+				"${workspaceFolder}/flix/led.ino",
+				"${workspaceFolder}/flix/log.ino",
+				"${workspaceFolder}/flix/mavlink.ino",
+				"${workspaceFolder}/flix/motors.ino",
+				"${workspaceFolder}/flix/rc.ino",
+				"${workspaceFolder}/flix/time.ino",
+				"${workspaceFolder}/flix/wifi.ino"
+			],
+			"compilerPath": "~/AppData/Local/Arduino15/packages/esp32/tools/esp-x32/2411/bin/xtensa-esp32-elf-g++.exe",
+			"cStandard": "c11",
+			"cppStandard": "c++17",
+			"defines": [
+				"F_CPU=240000000L",
+				"ARDUINO=10607",
+				"ARDUINO_D1_MINI32",
+				"ARDUINO_ARCH_ESP32",
+				"ARDUINO_BOARD=D1_MINI32",
+				"ARDUINO_VARIANT=d1_mini32",
+				"ARDUINO_PARTITION_default",
+				"ARDUINO_FQBN=esp32:esp32:d1_mini32",
+				"ESP32",
+				"CORE_DEBUG_LEVEL=0",
+				"ARDUINO_USB_CDC_ON_BOOT="
+			]
+		}
+	],
+	"version": 4
+}

.vscode/extensions.json

@@ -0,0 +1,9 @@
+{
+	// See https://go.microsoft.com/fwlink/?LinkId=827846 to learn about workspace recommendations.
+	"recommendations": [
+		"ms-vscode.cpptools",
+		"ms-vscode.cmake-tools",
+		"ms-python.python"
+	],
+	"unwantedRecommendations": []
+}

.vscode/intellisense.h

@@ -0,0 +1,5 @@
+#ifdef __INTELLISENSE__
+	#pragma diag_suppress 144, 513
+	// diag 144: a value of type "enum <unnamed>" cannot be used to initialize an entity of type "enum <unnamed>"C/C++
+	// diag 513: a value of type "enum <unnamed>" cannot be assigned to an entity of type "enum <unnamed>"C/C++
+#endif

.vscode/launch.json

@@ -0,0 +1,25 @@
+{
+	"version": "0.2.0",
+	"configurations": [
+		{
+			"name": "Debug simulation",
+			"type": "cppdbg",
+			"request": "launch",
+			"program": "/usr/bin/gzserver",
+			"osx": {
+				"program": "/opt/homebrew/bin/gzserver",
+				"MIMode": "lldb",
+			},
+			"args": ["--verbose", "${workspaceFolder}/gazebo/flix.world"],
+			"stopAtEntry": false,
+			"cwd": "${fileDirname}",
+			"environment": [
+				{"name": "GAZEBO_MODEL_PATH", "value": "${workspaceFolder}/gazebo/models"},
+				{"name": "GAZEBO_PLUGIN_PATH", "value": "${workspaceFolder}/gazebo/build"}
+			],
+			"MIMode": "gdb",
+			"preLaunchTask": "Build simulator",
+			"externalConsole": true,
+		},
+	]
+}

.vscode/settings.json

@@ -0,0 +1,13 @@
+{
+	"C_Cpp.intelliSenseEngineFallback": "enabled",
+	"files.associations": {
+		"*.sdf": "xml",
+		"*.ino": "cpp",
+		"*.h": "cpp"
+	},
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.function": "newLine",
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.block": "sameLine",
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.lambda": "sameLine",
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.namespace": "sameLine",
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.type": "sameLine"
+}

.vscode/tasks.json

@@ -0,0 +1,31 @@
+{
+	"tasks": [
+		{
+			"label": "Build firmware",
+			"type": "shell",
+			"command": "make",
+			"problemMatcher": [ "$gcc" ],
+			"presentation": { "clear": true, "showReuseMessage": false },
+		},
+		{
+			"label": "Upload firmware",
+			"type": "shell",
+			"command": "make upload",
+			"problemMatcher": [ "$gcc" ],
+			"presentation": { "clear": true, "showReuseMessage": false }
+		},
+		{
+			"label": "Build simulator",
+			"type": "shell",
+			"command": "make build_simulator",
+			"problemMatcher": [ "$gcc" ],
+			"presentation": { "clear": true, "showReuseMessage": false }
+		},
+		{
+			"label": "Clean",
+			"type": "shell",
+			"command": "make clean",
+		}
+	],
+	"version": "2.0.0"
+}

CNAME

@@ -1 +0,0 @@
-quadcopter.dev

Makefile

@@ -0,0 +1,43 @@
+BOARD = esp32:esp32:d1_mini32
+PORT := $(wildcard /dev/serial/by-id/usb-Silicon_Labs_CP21* /dev/serial/by-id/usb-1a86_USB_Single_Serial_* /dev/cu.usbserial-*)
+PORT := $(strip $(PORT))
+
+build: .dependencies
+	arduino-cli compile --fqbn $(BOARD) flix
+
+upload: build
+	arduino-cli upload --fqbn $(BOARD) -p "$(PORT)" flix
+
+monitor:
+	arduino-cli monitor -p "$(PORT)" -c baudrate=115200
+
+dependencies .dependencies:
+	arduino-cli core update-index --config-file arduino-cli.yaml
+	arduino-cli core install esp32:esp32@3.2.0 --config-file arduino-cli.yaml
+	arduino-cli lib update-index
+	arduino-cli lib install "FlixPeriph"
+	arduino-cli lib install "MAVLink"@2.0.16
+	touch .dependencies
+
+gazebo/build cmake: gazebo/CMakeLists.txt
+	mkdir -p gazebo/build
+	cd gazebo/build && cmake ..
+
+build_simulator: .dependencies gazebo/build
+	make -C gazebo/build
+
+simulator: build_simulator
+	GAZEBO_MODEL_PATH=$$GAZEBO_MODEL_PATH:${CURDIR}/gazebo/models \
+	GAZEBO_PLUGIN_PATH=$$GAZEBO_PLUGIN_PATH:${CURDIR}/gazebo/build \
+	gazebo --verbose ${CURDIR}/gazebo/flix.world
+
+log:
+	PORT=$(PORT) tools/grab_log.py
+
+plot:
+	plotjuggler -d $(shell ls -t tools/log/*.csv | head -n1)
+
+clean:
+	rm -rf gazebo/build flix/build flix/cache .dependencies
+
+.PHONY: build upload monitor dependencies cmake build_simulator simulator log clean

README.md

@@ -0,0 +1,7 @@
+# Flix
+
+Minimal **Flix** quadcopter firmware implementation for the [book](https://quadcopter.dev).
+
+See the full code and documentation in the main branch: https://github.com/okalachev/flix.
+
+<img src="docs/img/flix1.jpg" width=500 alt="Flix quadcopter">

arduino-cli.yaml

@@ -0,0 +1,3 @@
+board_manager:
+  additional_urls:
+    - https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json

docs/assets/washer-m3.step

@@ -0,0 +1,200 @@
+ISO-10303-21;
+HEADER;
+
+FILE_DESCRIPTION(
+/* description */ (''),
+/* implementation_level */ '2;1');
+
+FILE_NAME(
+/* name */ 'washer-m3.step',
+/* time_stamp */ '2024-10-29T13:59:42+03:00',
+/* author */ (''),
+/* organization */ (''),
+/* preprocessor_version */ '',
+/* originating_system */ '',
+
+/* authorisation */ '');
+
+FILE_SCHEMA (('AUTOMOTIVE_DESIGN { 1 0 10303 214 3 1 1 }'));
+ENDSEC;
+
+DATA;
+#10=MECHANICAL_DESIGN_GEOMETRIC_PRESENTATION_REPRESENTATION('',(#13),#125);
+#11=SHAPE_REPRESENTATION_RELATIONSHIP('SRR','None',#132,#12);
+#12=ADVANCED_BREP_SHAPE_REPRESENTATION('',(#14),#124);
+#13=STYLED_ITEM('',(#141),#14);
+#14=MANIFOLD_SOLID_BREP('Body1',#65);
+#15=FACE_BOUND('',#26,.T.);
+#16=FACE_BOUND('',#28,.T.);
+#17=PLANE('',#85);
+#18=PLANE('',#86);
+#19=FACE_OUTER_BOUND('',#23,.T.);
+#20=FACE_OUTER_BOUND('',#24,.T.);
+#21=FACE_OUTER_BOUND('',#25,.T.);
+#22=FACE_OUTER_BOUND('',#27,.T.);
+#23=EDGE_LOOP('',(#47,#48,#49,#50));
+#24=EDGE_LOOP('',(#51,#52,#53,#54));
+#25=EDGE_LOOP('',(#55));
+#26=EDGE_LOOP('',(#56));
+#27=EDGE_LOOP('',(#57));
+#28=EDGE_LOOP('',(#58));
+#29=LINE('',#112,#31);
+#30=LINE('',#118,#32);
+#31=VECTOR('',#93,1.7);
+#32=VECTOR('',#100,2.7);
+#33=CIRCLE('',#80,1.7);
+#34=CIRCLE('',#81,1.7);
+#35=CIRCLE('',#83,2.7);
+#36=CIRCLE('',#84,2.7);
+#37=VERTEX_POINT('',#109);
+#38=VERTEX_POINT('',#111);
+#39=VERTEX_POINT('',#115);
+#40=VERTEX_POINT('',#117);
+#41=EDGE_CURVE('',#37,#37,#33,.T.);
+#42=EDGE_CURVE('',#37,#38,#29,.T.);
+#43=EDGE_CURVE('',#38,#38,#34,.T.);
+#44=EDGE_CURVE('',#39,#39,#35,.T.);
+#45=EDGE_CURVE('',#39,#40,#30,.T.);
+#46=EDGE_CURVE('',#40,#40,#36,.T.);
+#47=ORIENTED_EDGE('',*,*,#41,.F.);
+#48=ORIENTED_EDGE('',*,*,#42,.T.);
+#49=ORIENTED_EDGE('',*,*,#43,.T.);
+#50=ORIENTED_EDGE('',*,*,#42,.F.);
+#51=ORIENTED_EDGE('',*,*,#44,.F.);
+#52=ORIENTED_EDGE('',*,*,#45,.T.);
+#53=ORIENTED_EDGE('',*,*,#46,.T.);
+#54=ORIENTED_EDGE('',*,*,#45,.F.);
+#55=ORIENTED_EDGE('',*,*,#44,.T.);
+#56=ORIENTED_EDGE('',*,*,#41,.T.);
+#57=ORIENTED_EDGE('',*,*,#46,.F.);
+#58=ORIENTED_EDGE('',*,*,#43,.F.);
+#59=CYLINDRICAL_SURFACE('',#79,1.7);
+#60=CYLINDRICAL_SURFACE('',#82,2.7);
+#61=ADVANCED_FACE('',(#19),#59,.F.);
+#62=ADVANCED_FACE('',(#20),#60,.T.);
+#63=ADVANCED_FACE('',(#21,#15),#17,.T.);
+#64=ADVANCED_FACE('',(#22,#16),#18,.F.);
+#65=CLOSED_SHELL('',(#61,#62,#63,#64));
+#66=DERIVED_UNIT_ELEMENT(#68,1.);
+#67=DERIVED_UNIT_ELEMENT(#127,-3.);
+#68=(
+MASS_UNIT()
+NAMED_UNIT(*)
+SI_UNIT(.KILO.,.GRAM.)
+);
+#69=DERIVED_UNIT((#66,#67));
+#70=MEASURE_REPRESENTATION_ITEM('density measure',
+POSITIVE_RATIO_MEASURE(7850.),#69);
+#71=PROPERTY_DEFINITION_REPRESENTATION(#76,#73);
+#72=PROPERTY_DEFINITION_REPRESENTATION(#77,#74);
+#73=REPRESENTATION('material name',(#75),#124);
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docs/build.md

@@ -0,0 +1,175 @@
+# Building and running
+
+To build the firmware or the simulator, you need to clone the repository using git:
+
+```bash
+git clone https://github.com/okalachev/flix.git
+cd flix
+```
+
+## Simulation
+
+### Ubuntu
+
+The latest version of Ubuntu supported by Gazebo 11 simulator is 22.04. If you have a newer version, consider using a virtual machine.
+
+1. Install Arduino CLI:
+
+   ```bash
+   curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=~/.local/bin sh
+   ```
+
+2. Install Gazebo 11:
+
+   ```bash
+   curl -sSL http://get.gazebosim.org | sh
+   ```
+
+   Set up your Gazebo environment variables:
+
+   ```bash
+   echo "source /usr/share/gazebo/setup.sh" >> ~/.bashrc
+   source ~/.bashrc
+   ```
+
+3. Install SDL2 and other dependencies:
+
+   ```bash
+   sudo apt-get update && sudo apt-get install build-essential libsdl2-dev
+   ```
+
+4. Add your user to the `input` group to enable joystick support (you need to re-login after this command):
+
+   ```bash
+   sudo usermod -a -G input $USER
+   ```
+
+5. Run the simulation:
+
+   ```bash
+   make simulator
+   ```
+
+### macOS
+
+1. Install Homebrew package manager, if you don't have it installed:
+
+   ```bash
+   /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
+   ```
+
+2. Install Arduino CLI, Gazebo 11 and SDL2:
+
+   ```bash
+   brew tap osrf/simulation
+   brew install arduino-cli
+   brew install gazebo11
+   brew install sdl2
+   ```
+
+   Set up your Gazebo environment variables:
+
+   ```bash
+   echo "source /opt/homebrew/share/gazebo/setup.sh" >> ~/.zshrc
+   source ~/.zshrc
+   ```
+
+3. Run the simulation:
+
+   ```bash
+   make simulator
+   ```
+
+### Setup and flight
+
+#### Control with smartphone
+
+1. Install [QGroundControl mobile app](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/getting_started/download_and_install.html#android) on your smartphone.
+2. Connect your smartphone to the same Wi-Fi network as the machine running the simulator.
+3. If you're using a virtual machine, make sure that its network is set to the **bridged** mode with Wi-Fi adapter selected.
+4. Run the simulation.
+5. Open QGroundControl app. It should connect and begin showing the virtual drone's telemetry automatically.
+6. Go to the settings and enable *Virtual Joystick*. *Auto-Center Throttle* setting **should be disabled**.
+7. Use the virtual joystick to fly the drone!
+
+#### Control with USB remote control
+
+1. Connect your USB remote control to the machine running the simulator.
+2. Run the simulation.
+3. Calibrate the RC using `cr` command in the command line interface and stop the simulation.
+4. Copy the calibration results to the source code (`gazebo/joystick.h`).
+5. Run the simulation again.
+6. Use the USB remote control to fly the drone!
+
+## Firmware
+
+### Arduino IDE (Windows, Linux, macOS)
+
+1. Install [Arduino IDE](https://www.arduino.cc/en/software) (version 2 is recommended).
+2. Windows users might need to install [USB to UART bridge driver from Silicon Labs](https://www.silabs.com/developers/usb-to-uart-bridge-vcp-drivers).
+3. Install ESP32 core, version 3.2.0. See the [official Espressif's instructions](https://docs.espressif.com/projects/arduino-esp32/en/latest/installing.html#installing-using-arduino-ide) on installing ESP32 Core in Arduino IDE.
+4. Install the following libraries using [Library Manager](https://docs.arduino.cc/software/ide-v2/tutorials/ide-v2-installing-a-library):
+   * `FlixPeriph`, the latest version.
+   * `MAVLink`, version 2.0.16.
+5. Clone the project using git or [download the source code as a ZIP archive](https://codeload.github.com/okalachev/flix/zip/refs/heads/master).
+6. Open the downloaded Arduino sketch `flix/flix.ino` in Arduino IDE.
+7. Connect your ESP32 board to the computer and choose correct board type in Arduino IDE (*WEMOS D1 MINI ESP32* for ESP32 Mini) and the port.
+8. [Build and upload](https://docs.arduino.cc/software/ide-v2/tutorials/getting-started/ide-v2-uploading-a-sketch) the firmware using Arduino IDE.
+
+### Command line (Windows, Linux, macOS)
+
+1. [Install Arduino CLI](https://arduino.github.io/arduino-cli/installation/).
+2. Windows users might need to install [USB to UART bridge driver from Silicon Labs](https://www.silabs.com/developers/usb-to-uart-bridge-vcp-drivers).
+3. Compile the firmware using `make`. Arduino dependencies will be installed automatically:
+
+   ```bash
+   make
+   ```
+
+   You can flash the firmware to the board using command:
+
+   ```bash
+   make upload
+   ```
+
+   You can also compile the firmware, upload it and start serial port monitoring using command:
+
+   ```bash
+   make upload monitor
+   ```
+
+See other available Make commands in the [Makefile](../Makefile).
+
+### Setup and flight
+
+Before flight you need to calibrate the accelerometer:
+
+1. Open Serial Monitor in Arduino IDE (use use `make monitor` command in the command line).
+2. Type `ca` command there.
+3. Copy calibration results to the source code (`flix/imu.ino`).
+
+#### Control with smartphone
+
+1. Install [QGroundControl mobile app](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/getting_started/download_and_install.html#android) on your smartphone.
+2. Power the drone using the battery.
+3. Connect your smartphone to the appeared `flix` Wi-Fi network.
+4. Open QGroundControl app. It should connect and begin showing the drone's telemetry automatically.
+5. Go to the settings and enable *Virtual Joystick*. *Auto-Center Throttle* setting **should be disabled**.
+6. Use the virtual joystick to fly the drone!
+
+#### Control with remote control
+
+Before flight using remote control, you need to calibrate it:
+
+1. Open Serial Monitor in Arduino IDE (use use `make monitor` command in the command line).
+2. Type `cr` command there.
+3. Copy calibration results to the source code (`flix/rc.ino`).
+
+Then you can use your remote control to fly the drone!
+
+> [!NOTE]
+> If something goes wrong, go to the [Troubleshooting](troubleshooting.md) article.
+
+### Firmware code structure
+
+See [firmware overview](firmware.md) for more details.

docs/firmware.md

@@ -0,0 +1,37 @@
+# Firmware overview
+
+## Dataflow
+
+<img src="img/dataflow.svg" width=800 alt="Firmware dataflow diagram">
+
+The main loop is running at 1000 Hz. All the dataflow is happening through global variables (for simplicity):
+
+* `t` *(float)* — current step time, *s*.
+* `dt` *(float)* — time delta between the current and previous steps, *s*.
+* `gyro` *(Vector)* — data from the gyroscope, *rad/s*.
+* `acc` *(Vector)* — acceleration data from the accelerometer, *m/s<sup>2</sup>*.
+* `rates` *(Vector)* — filtered angular rates, *rad/s*.
+* `attitude` *(Quaternion)* — estimated attitude (orientation) of drone.
+* `controlRoll`, `controlPitch`, ... *(float[])* — pilot's control inputs, range [-1, 1].
+* `motors` *(float[])* — motor outputs, normalized to [0, 1] range; reverse rotation is possible.
+
+## Source files
+
+Firmware source files are located in `flix` directory. The key files are:
+
+* [`flix.ino`](../flix/flix.ino) — main entry point, Arduino sketch. Includes global variables definition and the main loop.
+* [`imu.ino`](../flix/imu.ino) — reading data from the IMU sensor (gyroscope and accelerometer), IMU calibration.
+* [`rc.ino`](../flix/rc.ino) — reading data from the RC receiver, RC calibration.
+* [`estimate.ino`](../flix/estimate.ino) — drone's attitude estimation, complementary filter.
+* [`control.ino`](../flix/control.ino) — drone's attitude and rates control, three-dimensional two-level cascade PID controller.
+* [`motors.ino`](../flix/motors.ino) — PWM motor outputs control.
+
+Utility files include:
+
+* [`vector.h`](../flix/vector.h), [`quaternion.h`](../flix/quaternion.h) — project's vector and quaternion libraries implementation.
+* [`pid.h`](../flix/pid.h) — generic PID controller implementation.
+* [`lpf.h`](../flix/lpf.h) — generic low-pass filter implementation.
+
+## Building
+
+See build instructions in [build.md](build.md).

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docs/log.md

@@ -0,0 +1,72 @@
+# Log analysis
+
+Flix quadcopter uses RAM to store flight log data. The default log capacity is 10 seconds at 100 Hz. This configuration can be adjusted in the `log.ino` file.
+
+To perform log analysis, you need to download the log right after the flight without powering off the drone. Then you can use several tools to analyze the log data.
+
+## Log download
+
+To download the log, connect the ESP32 using USB right after the flight and run the following command:
+
+```bash
+make log
+```
+
+Logs are stored in `tools/log/*.csv` files.
+
+## Analysis
+
+### PlotJuggler
+
+The recommended tool for log analysis is PlotJuggler.
+
+<img src="img/plotjuggler.png" width="500">
+
+1. Install PlotJuggler using the [official instructions](https://github.com/facontidavide/PlotJuggler?tab=readme-ov-file#installation).
+
+2. Run PlotJuggler and drag'n'drop the downloaded log file there. Choose `t` column to be used as X axis.
+
+   You can open the most recent downloaded file using the command:
+
+   ```bash
+   make plot
+   ```
+
+   You can perform both log download and run PlotJuggler in one command:
+
+   ```bash
+   make log plot
+   ```
+
+### FlightPlot
+
+FlightPlot is a powerful tool for analyzing logs in [ULog format](https://docs.px4.io/main/en/dev_log/ulog_file_format.html). This format is used in PX4 and ArduPilot flight software.
+
+<img src="img/flightplot.png" width="500">
+
+1. [Install FlightPlot](https://github.com/PX4/FlightPlot).
+2. Flix repository contains a tool for converting CSV logs to ULog format. Build the tool using [the instructions](../tools/csv_to_ulog/README.md) and convert the log you want to analyze.
+3. Run FlightPlot and drag'n'drop the converted ULog-file there.
+
+### Foxglove Studio
+
+Foxglove is a tool for visualizing and analyzing robotics data with very rich functionality. It can import various formats, but mainly focuses on its own format, called [MCAP](https://mcap.dev).
+
+<img src="img/foxglove.png" width="500">
+
+1. Install Foxglove Studio from the [official website](https://foxglove.dev/download).
+
+2. Flix repository contains a tool for converting CSV logs to MCAP format. First, install its dependencies:
+
+   ```bash
+   cd tools
+   pip install -r requirements.txt
+   ```
+
+3. Convert the log you want to analyze:
+
+   ```bash
+   csv_to_mcap.py log_file.csv
+   ```
+
+4. Open the log in Foxglove Studio using *Open local file* command.

flix/cli.ino

@@ -0,0 +1,103 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Implementation of command line interface
+
+#include "pid.h"
+#include "vector.h"
+
+extern const int MOTOR_REAR_LEFT, MOTOR_REAR_RIGHT, MOTOR_FRONT_RIGHT, MOTOR_FRONT_LEFT;
+extern float loopRate;
+extern uint16_t channels[16];
+
+const char* motd =
+"\nWelcome to\n"
+" _______  __       __  ___   ___\n"
+"|   ____||  |     |  | \\  \\ /  /\n"
+"|  |__   |  |     |  |  \\  V  /\n"
+"|   __|  |  |     |  |   >   <\n"
+"|  |     |  `----.|  |  /  .  \\\n"
+"|__|     |_______||__| /__/ \\__\\\n\n"
+"Commands:\n\n"
+"help - show help\n"
+"ps - show pitch/roll/yaw\n"
+"psq - show attitude quaternion\n"
+"imu - show IMU data\n"
+"rc - show RC data\n"
+"mot - show motor output\n"
+"log - dump in-RAM log\n"
+"cr - calibrate RC\n"
+"cg - calibrate gyro\n"
+"ca - calibrate accel\n"
+"mfr, mfl, mrr, mrl - test motor (remove props)\n"
+"reset - reset drone's state\n";
+
+void doCommand(const String& command) {
+	if (command == "help" || command == "motd") {
+		Serial.println(motd);
+	} else if (command == "ps") {
+		Vector a = attitude.toEuler();
+		Serial.printf("roll: %f pitch: %f yaw: %f\n", a.x * RAD_TO_DEG, a.y * RAD_TO_DEG, a.z * RAD_TO_DEG);
+	} else if (command == "psq") {
+		Serial.printf("qx: %f qy: %f qz: %f qw: %f\n", attitude.x, attitude.y, attitude.z, attitude.w);
+	} else if (command == "imu") {
+		printIMUInfo();
+		Serial.printf("gyro: %f %f %f\n", rates.x, rates.y, rates.z);
+		Serial.printf("acc: %f %f %f\n", acc.x, acc.y, acc.z);
+		printIMUCalibration();
+		Serial.printf("rate: %f\n", loopRate);
+	} else if (command == "rc") {
+		Serial.printf("channels: ");
+		for (int i = 0; i < 16; i++) {
+			Serial.printf("%u ", channels[i]);
+		}
+		Serial.printf("\nroll: %g pitch: %g yaw: %g throttle: %g armed: %g mode: %g\n",
+			controlRoll, controlPitch, controlYaw, controlThrottle, controlArmed, controlMode);
+		Serial.printf("mode: %s\n", getModeName());
+	} else if (command == "mot") {
+		Serial.printf("front-right %f front-left %f rear-right %f rear-left %f\n",
+			motors[MOTOR_FRONT_RIGHT], motors[MOTOR_FRONT_LEFT], motors[MOTOR_REAR_RIGHT], motors[MOTOR_REAR_LEFT]);
+	} else if (command == "log") {
+		dumpLog();
+	} else if (command == "cr") {
+		calibrateRC();
+	} else if (command == "cg") {
+		calibrateGyro();
+	} else if (command == "ca") {
+		calibrateAccel();
+	} else if (command == "mfr") {
+		testMotor(MOTOR_FRONT_RIGHT);
+	} else if (command == "mfl") {
+		testMotor(MOTOR_FRONT_LEFT);
+	} else if (command == "mrr") {
+		testMotor(MOTOR_REAR_RIGHT);
+	} else if (command == "mrl") {
+		testMotor(MOTOR_REAR_LEFT);
+	} else if (command == "reset") {
+		attitude = Quaternion();
+	} else if (command == "") {
+		// do nothing
+	} else {
+		Serial.println("Invalid command: " + command);
+	}
+}
+
+void handleInput() {
+	static bool showMotd = true;
+	static String input;
+
+	if (showMotd) {
+		Serial.printf("%s\n", motd);
+		showMotd = false;
+	}
+
+	while (Serial.available()) {
+		char c = Serial.read();
+		if (c == '\n') {
+			doCommand(input);
+			input.clear();
+		} else {
+			input += c;
+		}
+	}
+}

flix/control.ino

@@ -0,0 +1,177 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Flight control
+
+#include "vector.h"
+#include "quaternion.h"
+#include "pid.h"
+#include "lpf.h"
+#include "util.h"
+
+#define PITCHRATE_P 0.05
+#define PITCHRATE_I 0.2
+#define PITCHRATE_D 0.001
+#define PITCHRATE_I_LIM 0.3
+#define ROLLRATE_P PITCHRATE_P
+#define ROLLRATE_I PITCHRATE_I
+#define ROLLRATE_D PITCHRATE_D
+#define ROLLRATE_I_LIM PITCHRATE_I_LIM
+#define YAWRATE_P 0.3
+#define YAWRATE_I 0.0
+#define YAWRATE_D 0.0
+#define YAWRATE_I_LIM 0.3
+#define ROLL_P 4.5
+#define ROLL_I 0
+#define ROLL_D 0
+#define PITCH_P ROLL_P
+#define PITCH_I ROLL_I
+#define PITCH_D ROLL_D
+#define YAW_P 3
+#define PITCHRATE_MAX radians(360)
+#define ROLLRATE_MAX radians(360)
+#define YAWRATE_MAX radians(300)
+#define TILT_MAX radians(30)
+
+#define RATES_D_LPF_ALPHA 0.2 // cutoff frequency ~ 40 Hz
+
+enum { MANUAL, ACRO, STAB, USER } mode = STAB;
+enum { YAW, YAW_RATE } yawMode = YAW;
+bool armed = false;
+
+PID rollRatePID(ROLLRATE_P, ROLLRATE_I, ROLLRATE_D, ROLLRATE_I_LIM, RATES_D_LPF_ALPHA);
+PID pitchRatePID(PITCHRATE_P, PITCHRATE_I, PITCHRATE_D, PITCHRATE_I_LIM, RATES_D_LPF_ALPHA);
+PID yawRatePID(YAWRATE_P, YAWRATE_I, YAWRATE_D);
+PID rollPID(ROLL_P, ROLL_I, ROLL_D);
+PID pitchPID(PITCH_P, PITCH_I, PITCH_D);
+PID yawPID(YAW_P, 0, 0);
+
+Quaternion attitudeTarget;
+Vector ratesTarget;
+Vector torqueTarget;
+float thrustTarget;
+
+extern const int MOTOR_REAR_LEFT, MOTOR_REAR_RIGHT, MOTOR_FRONT_RIGHT, MOTOR_FRONT_LEFT;
+
+void control() {
+	interpretRC();
+	failsafe();
+	if (mode == STAB) {
+		controlAttitude();
+		controlRate();
+		controlTorque();
+	} else if (mode == ACRO) {
+		controlRate();
+		controlTorque();
+	} else if (mode == MANUAL) {
+		controlTorque();
+	}
+}
+
+void interpretRC() {
+	armed = controlThrottle >= 0.05 && controlArmed >= 0.5;
+
+
+	// NOTE: put ACRO or MANUAL modes there if you want to use them
+	if (controlMode < 0.25) {
+		mode = STAB;
+	} else if (controlMode < 0.75) {
+		mode = STAB;
+	} else {
+		mode = STAB;
+	}
+
+	thrustTarget = controlThrottle;
+
+	if (mode == ACRO) {
+		yawMode = YAW_RATE;
+		ratesTarget.x = controlRoll * ROLLRATE_MAX;
+		ratesTarget.y = controlPitch * PITCHRATE_MAX;
+		ratesTarget.z = -controlYaw * YAWRATE_MAX; // positive yaw stick means clockwise rotation in FLU
+
+	} else if (mode == STAB) {
+		yawMode = controlYaw == 0 ? YAW : YAW_RATE;
+
+		attitudeTarget = Quaternion::fromEuler(Vector(
+			controlRoll * TILT_MAX,
+			controlPitch * TILT_MAX,
+			attitudeTarget.getYaw()));
+		ratesTarget.z = -controlYaw * YAWRATE_MAX; // positive yaw stick means clockwise rotation in FLU
+
+	} else if (mode == MANUAL) {
+		// passthrough mode
+		yawMode = YAW_RATE;
+		torqueTarget = Vector(controlRoll, controlPitch, -controlYaw) * 0.01;
+	}
+
+	if (yawMode == YAW_RATE || !motorsActive()) {
+		// update yaw target as we don't have control over the yaw
+		attitudeTarget.setYaw(attitude.getYaw());
+	}
+}
+
+void controlAttitude() {
+	if (!armed) {
+		rollPID.reset();
+		pitchPID.reset();
+		yawPID.reset();
+		return;
+	}
+
+	const Vector up(0, 0, 1);
+	Vector upActual = Quaternion::rotateVector(up, attitude);
+	Vector upTarget = Quaternion::rotateVector(up, attitudeTarget);
+
+	Vector error = Vector::rotationVectorBetween(upTarget, upActual);
+
+	ratesTarget.x = rollPID.update(error.x, dt);
+	ratesTarget.y = pitchPID.update(error.y, dt);
+
+	if (yawMode == YAW) {
+		float yawError = wrapAngle(attitudeTarget.getYaw() - attitude.getYaw());
+		ratesTarget.z = yawPID.update(yawError, dt);
+	}
+}
+
+void controlRate() {
+	if (!armed) {
+		rollRatePID.reset();
+		pitchRatePID.reset();
+		yawRatePID.reset();
+		return;
+	}
+
+	Vector error = ratesTarget - rates;
+
+	// Calculate desired torque, where 0 - no torque, 1 - maximum possible torque
+	torqueTarget.x = rollRatePID.update(error.x, dt);
+	torqueTarget.y = pitchRatePID.update(error.y, dt);
+	torqueTarget.z = yawRatePID.update(error.z, dt);
+}
+
+void controlTorque() {
+	if (!armed) {
+		memset(motors, 0, sizeof(motors));
+		return;
+	}
+
+	motors[MOTOR_FRONT_LEFT] = thrustTarget + torqueTarget.x - torqueTarget.y + torqueTarget.z;
+	motors[MOTOR_FRONT_RIGHT] = thrustTarget - torqueTarget.x - torqueTarget.y - torqueTarget.z;
+	motors[MOTOR_REAR_LEFT] = thrustTarget + torqueTarget.x + torqueTarget.y - torqueTarget.z;
+	motors[MOTOR_REAR_RIGHT] = thrustTarget - torqueTarget.x + torqueTarget.y + torqueTarget.z;
+
+	motors[0] = constrain(motors[0], 0, 1);
+	motors[1] = constrain(motors[1], 0, 1);
+	motors[2] = constrain(motors[2], 0, 1);
+	motors[3] = constrain(motors[3], 0, 1);
+}
+
+const char* getModeName() {
+	switch (mode) {
+		case MANUAL: return "MANUAL";
+		case ACRO: return "ACRO";
+		case STAB: return "STAB";
+		case USER: return "USER";
+		default: return "UNKNOWN";
+	}
+}

flix/estimate.ino

@@ -0,0 +1,42 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Attitude estimation from gyro and accelerometer
+
+#include "quaternion.h"
+#include "vector.h"
+#include "lpf.h"
+#include "util.h"
+
+#define WEIGHT_ACC 0.003
+#define RATES_LFP_ALPHA 0.2 // cutoff frequency ~ 40 Hz
+
+LowPassFilter<Vector> ratesFilter(RATES_LFP_ALPHA);
+
+void estimate() {
+	applyGyro();
+	applyAcc();
+}
+
+void applyGyro() {
+	// filter gyro to get angular rates
+	rates = ratesFilter.update(gyro);
+
+	// apply rates to attitude
+	attitude = Quaternion::rotate(attitude, Quaternion::fromRotationVector(rates * dt));
+}
+
+void applyAcc() {
+	// test should we apply accelerometer gravity correction
+	float accNorm = acc.norm();
+	bool landed = !motorsActive() && abs(accNorm - ONE_G) < ONE_G * 0.1f;
+
+	if (!landed) return;
+
+	// calculate accelerometer correction
+	Vector up = Quaternion::rotateVector(Vector(0, 0, 1), attitude);
+	Vector correction = Vector::rotationVectorBetween(acc, up) * WEIGHT_ACC;
+
+	// apply correction
+	attitude = Quaternion::rotate(attitude, Quaternion::fromRotationVector(correction));
+}

flix/failsafe.ino

@@ -0,0 +1,26 @@
+// Copyright (c) 2024 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Fail-safe for RC loss
+
+#define RC_LOSS_TIMEOUT 0.2
+#define DESCEND_TIME 3.0 // time to descend from full throttle to zero
+
+extern float controlTime;
+
+// RC loss failsafe
+void failsafe() {
+	if (t - controlTime > RC_LOSS_TIMEOUT) {
+		descend();
+	}
+}
+
+// Smooth descend on RC lost
+void descend() {
+	mode = STAB;
+	controlRoll = 0;
+	controlPitch = 0;
+	controlYaw = 0;
+	controlThrottle -= dt / DESCEND_TIME;
+	if (controlThrottle < 0) controlThrottle = 0;
+}

flix/flix.ino

@@ -0,0 +1,50 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Main firmware file
+
+#include "vector.h"
+#include "quaternion.h"
+#include "util.h"
+
+#define SERIAL_BAUDRATE 115200
+#define WIFI_ENABLED 1
+
+float t = NAN; // current step time, s
+float dt; // time delta from previous step, s
+float controlRoll, controlPitch, controlYaw, controlThrottle, controlArmed, controlMode; // pilot's inputs, range [-1, 1]
+Vector gyro; // gyroscope data
+Vector acc; // accelerometer data, m/s/s
+Vector rates; // filtered angular rates, rad/s
+Quaternion attitude; // estimated attitude
+float motors[4]; // normalized motors thrust in range [0..1]
+
+void setup() {
+	Serial.begin(SERIAL_BAUDRATE);
+	Serial.println("Initializing flix\n");
+	disableBrownOut();
+	setupLED();
+	setupMotors();
+	setLED(true);
+#if WIFI_ENABLED
+	setupWiFi();
+#endif
+	setupIMU();
+	setupRC();
+	setLED(false);
+	Serial.println("Initializing complete\n");
+}
+
+void loop() {
+	readIMU();
+	step();
+	readRC();
+	estimate();
+	control();
+	sendMotors();
+	handleInput();
+#if WIFI_ENABLED
+	processMavlink();
+#endif
+	logData();
+}

flix/imu.ino

@@ -0,0 +1,138 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Work with the IMU sensor
+
+#include <SPI.h>
+#include <MPU9250.h>
+#include "util.h"
+
+MPU9250 IMU(SPI);
+
+// NOTE: use 'ca' command to calibrate the accelerometer and put the values here
+Vector accBias;
+Vector accScale(1, 1, 1);
+Vector gyroBias;
+
+void setupIMU() {
+	Serial.println("Setup IMU");
+	bool status = IMU.begin();
+	if (!status) {
+		while (true) {
+			Serial.println("IMU begin error");
+			delay(1000);
+		}
+	}
+	configureIMU();
+	calibrateGyro();
+}
+
+void configureIMU() {
+	IMU.setAccelRange(IMU.ACCEL_RANGE_4G);
+	IMU.setGyroRange(IMU.GYRO_RANGE_2000DPS);
+	IMU.setDLPF(IMU.DLPF_MAX);
+	IMU.setRate(IMU.RATE_1KHZ_APPROX);
+}
+
+void readIMU() {
+	IMU.waitForData();
+	IMU.getGyro(gyro.x, gyro.y, gyro.z);
+	IMU.getAccel(acc.x, acc.y, acc.z);
+	// apply scale and bias
+	acc = (acc - accBias) / accScale;
+	gyro = gyro - gyroBias;
+	// rotate
+	rotateIMU(acc);
+	rotateIMU(gyro);
+}
+
+void rotateIMU(Vector& data) {
+	// Rotate from LFD to FLU
+	// NOTE: In case of using other IMU orientation, change this line:
+	data = Vector(data.y, data.x, -data.z);
+	// Axes orientation for various boards: https://github.com/okalachev/flixperiph#imu-axes-orientation
+}
+
+void calibrateGyro() {
+	const int samples = 1000;
+	Serial.println("Calibrating gyro, stand still");
+	IMU.setGyroRange(IMU.GYRO_RANGE_250DPS); // the most sensitive mode
+
+	gyroBias = Vector(0, 0, 0);
+	for (int i = 0; i < samples; i++) {
+		IMU.waitForData();
+		IMU.getGyro(gyro.x, gyro.y, gyro.z);
+		gyroBias = gyroBias + gyro;
+	}
+	gyroBias = gyroBias / samples;
+
+	printIMUCalibration();
+	configureIMU();
+}
+
+void calibrateAccel() {
+	Serial.println("Calibrating accelerometer");
+	IMU.setAccelRange(IMU.ACCEL_RANGE_2G); // the most sensitive mode
+
+	Serial.setTimeout(60000);
+	Serial.print("1/6 Place level [enter] ");
+	Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("2/6 Place nose up [enter] ");
+	Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("3/6 Place nose down [enter] ");
+	Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("4/6 Place on right side [enter] ");
+	Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("5/6 Place on left side [enter] ");
+	Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("6/6 Place upside down [enter] ");
+	Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+
+	printIMUCalibration();
+	Serial.print("✓ Calibration done!\n");
+	configureIMU();
+}
+
+void calibrateAccelOnce() {
+	const int samples = 1000;
+	static Vector accMax(-INFINITY, -INFINITY, -INFINITY);
+	static Vector accMin(INFINITY, INFINITY, INFINITY);
+
+	// Compute the average of the accelerometer readings
+	acc = Vector(0, 0, 0);
+	for (int i = 0; i < samples; i++) {
+		IMU.waitForData();
+		Vector sample;
+		IMU.getAccel(sample.x, sample.y, sample.z);
+		acc = acc + sample;
+	}
+	acc = acc / samples;
+
+	// Update the maximum and minimum values
+	if (acc.x > accMax.x) accMax.x = acc.x;
+	if (acc.y > accMax.y) accMax.y = acc.y;
+	if (acc.z > accMax.z) accMax.z = acc.z;
+	if (acc.x < accMin.x) accMin.x = acc.x;
+	if (acc.y < accMin.y) accMin.y = acc.y;
+	if (acc.z < accMin.z) accMin.z = acc.z;
+	// Compute scale and bias
+	accScale = (accMax - accMin) / 2 / ONE_G;
+	accBias = (accMax + accMin) / 2;
+}
+
+void printIMUCalibration() {
+	Serial.printf("gyro bias: %f %f %f\n", gyroBias.x, gyroBias.y, gyroBias.z);
+	Serial.printf("accel bias: %f %f %f\n", accBias.x, accBias.y, accBias.z);
+	Serial.printf("accel scale: %f %f %f\n", accScale.x, accScale.y, accScale.z);
+}
+
+void printIMUInfo() {
+	Serial.printf("model: %s\n", IMU.getModel());
+	Serial.printf("who am I: 0x%02X\n", IMU.whoAmI());
+}

flix/led.ino

@@ -0,0 +1,23 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Board's LED control
+
+#define BLINK_PERIOD 500000
+
+#ifndef LED_BUILTIN
+#define LED_BUILTIN 2 // for ESP32 Dev Module
+#endif
+
+void setupLED() {
+	pinMode(LED_BUILTIN, OUTPUT);
+}
+
+void setLED(bool on) {
+	static bool state = false;
+	if (on == state) {
+		return; // don't call digitalWrite if the state is the same
+	}
+	digitalWrite(LED_BUILTIN, on ? HIGH : LOW);
+	state = on;
+}

flix/log.ino

@@ -0,0 +1,53 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// In-RAM logging
+
+#define LOG_RATE 100
+#define LOG_DURATION 10
+#define LOG_PERIOD 1.0 / LOG_RATE
+#define LOG_SIZE LOG_DURATION * LOG_RATE
+#define LOG_COLUMNS 14
+
+float logBuffer[LOG_SIZE][LOG_COLUMNS]; // * 4 (float)
+int logPointer = 0;
+
+void logData() {
+	if (!armed) return;
+
+	static float logTime = 0;
+	if (t - logTime < LOG_PERIOD) return;
+	logTime = t;
+
+	logBuffer[logPointer][0] = t;
+	logBuffer[logPointer][1] = rates.x;
+	logBuffer[logPointer][2] = rates.y;
+	logBuffer[logPointer][3] = rates.z;
+	logBuffer[logPointer][4] = ratesTarget.x;
+	logBuffer[logPointer][5] = ratesTarget.y;
+	logBuffer[logPointer][6] = ratesTarget.z;
+	logBuffer[logPointer][7] = attitude.toEuler().x;
+	logBuffer[logPointer][8] = attitude.toEuler().y;
+	logBuffer[logPointer][9] = attitude.toEuler().z;
+	logBuffer[logPointer][10] = attitudeTarget.toEuler().x;
+	logBuffer[logPointer][11] = attitudeTarget.toEuler().y;
+	logBuffer[logPointer][12] = attitudeTarget.toEuler().z;
+	logBuffer[logPointer][13] = thrustTarget;
+
+	logPointer++;
+	if (logPointer >= LOG_SIZE) {
+		logPointer = 0;
+	}
+}
+
+void dumpLog() {
+	Serial.printf("t,rates.x,rates.y,rates.z,ratesTarget.x,ratesTarget.y,ratesTarget.z,"
+		"attitude.x,attitude.y,attitude.z,attitudeTarget.x,attitudeTarget.y,attitudeTarget.z,thrustTarget\n");
+	for (int i = 0; i < LOG_SIZE; i++) {
+		if (logBuffer[i][0] == 0) continue; // skip empty records
+		for (int j = 0; j < LOG_COLUMNS - 1; j++) {
+			Serial.printf("%f,", logBuffer[i][j]);
+		}
+		Serial.printf("%f\n", logBuffer[i][LOG_COLUMNS - 1]);
+	}
+}

flix/lpf.h

@@ -0,0 +1,39 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Low pass filter implementation
+
+#pragma once
+
+template <typename T> // Using template to make the filter usable for scalar and vector values
+class LowPassFilter {
+public:
+	float alpha; // smoothing constant, 1 means filter disabled
+	T output;
+
+	LowPassFilter(float alpha): alpha(alpha) {};
+
+	T update(const T input) {
+		if (alpha == 1) { // filter disabled
+			return input;
+		}
+
+		if (!initialized) {
+			output = input;
+			initialized = true;
+		}
+
+		return output += alpha * (input - output);
+	}
+
+	void setCutOffFrequency(float cutOffFreq, float dt) {
+		alpha = 1 - exp(-2 * PI * cutOffFreq * dt);
+	}
+
+	void reset() {
+		initialized = false;
+	}
+
+private:
+	bool initialized = false;
+};

flix/mavlink.ino

@@ -0,0 +1,102 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// MAVLink communication
+
+#if WIFI_ENABLED
+
+#include <MAVLink.h>
+
+#define SYSTEM_ID 1
+#define PERIOD_SLOW 1.0
+#define PERIOD_FAST 0.1
+#define MAVLINK_CONTROL_SCALE 0.7f
+#define MAVLINK_CONTROL_YAW_DEAD_ZONE 0.1f
+
+extern float controlTime;
+
+void processMavlink() {
+	sendMavlink();
+	receiveMavlink();
+}
+
+void sendMavlink() {
+	static float lastSlow = 0;
+	static float lastFast = 0;
+
+	mavlink_message_t msg;
+	uint32_t time = t * 1000;
+
+	if (t - lastSlow >= PERIOD_SLOW) {
+		lastSlow = t;
+
+		mavlink_msg_heartbeat_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg, MAV_TYPE_QUADROTOR, MAV_AUTOPILOT_GENERIC,
+			MAV_MODE_FLAG_MANUAL_INPUT_ENABLED | (armed * MAV_MODE_FLAG_SAFETY_ARMED) | ((mode == STAB) * MAV_MODE_FLAG_STABILIZE_ENABLED),
+			0, MAV_STATE_STANDBY);
+		sendMessage(&msg);
+	}
+
+	if (t - lastFast >= PERIOD_FAST) {
+		lastFast = t;
+
+		const float zeroQuat[] = {0, 0, 0, 0};
+		mavlink_msg_attitude_quaternion_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg,
+			time, attitude.w, attitude.x, -attitude.y, -attitude.z, rates.x, -rates.y, -rates.z, zeroQuat); // convert to frd
+		sendMessage(&msg);
+
+		mavlink_msg_rc_channels_raw_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg, controlTime * 1000, 0,
+			channels[0], channels[1], channels[2], channels[3], channels[4], channels[5], channels[6], channels[7], UINT8_MAX);
+		sendMessage(&msg);
+
+		float actuator[32];
+		memcpy(actuator, motors, sizeof(motors));
+		mavlink_msg_actuator_output_status_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg, time, 4, actuator);
+		sendMessage(&msg);
+
+		mavlink_msg_scaled_imu_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg, time,
+			acc.x * 1000, -acc.y * 1000, -acc.z * 1000, // convert to frd
+			gyro.x * 1000, -gyro.y * 1000, -gyro.z * 1000,
+			0, 0, 0, 0);
+		sendMessage(&msg);
+	}
+}
+
+void sendMessage(const void *msg) {
+	uint8_t buf[MAVLINK_MAX_PACKET_LEN];
+	int len = mavlink_msg_to_send_buffer(buf, (mavlink_message_t *)msg);
+	sendWiFi(buf, len);
+}
+
+void receiveMavlink() {
+	uint8_t buf[MAVLINK_MAX_PACKET_LEN];
+	int len = receiveWiFi(buf, MAVLINK_MAX_PACKET_LEN);
+
+	// New packet, parse it
+	mavlink_message_t msg;
+	mavlink_status_t status;
+	for (int i = 0; i < len; i++) {
+		if (mavlink_parse_char(MAVLINK_COMM_0, buf[i], &msg, &status)) {
+			handleMavlink(&msg);
+		}
+	}
+}
+
+void handleMavlink(const void *_msg) {
+	const mavlink_message_t& msg = *(mavlink_message_t *)_msg;
+
+	if (msg.msgid == MAVLINK_MSG_ID_MANUAL_CONTROL) {
+		mavlink_manual_control_t m;
+		mavlink_msg_manual_control_decode(&msg, &m);
+		controlThrottle = m.z / 1000.0f;
+		controlPitch = m.x / 1000.0f * MAVLINK_CONTROL_SCALE;
+		controlRoll = m.y / 1000.0f * MAVLINK_CONTROL_SCALE;
+		controlYaw = m.r / 1000.0f * MAVLINK_CONTROL_SCALE;
+		controlMode = 1; // STAB mode
+		controlArmed = 1; // armed
+		controlTime = t;
+
+		if (abs(controlYaw) < MAVLINK_CONTROL_YAW_DEAD_ZONE) controlYaw = 0;
+	}
+}
+
+#endif

flix/motors.ino

@@ -0,0 +1,61 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Motors output control using MOSFETs
+
+#include "util.h"
+
+#define MOTOR_0_PIN 12 // rear left
+#define MOTOR_1_PIN 13 // rear right
+#define MOTOR_2_PIN 14 // front right
+#define MOTOR_3_PIN 15 // front left
+
+#define PWM_FREQUENCY 78000
+#define PWM_RESOLUTION 10
+
+// Motors array indexes:
+const int MOTOR_REAR_LEFT = 0;
+const int MOTOR_REAR_RIGHT = 1;
+const int MOTOR_FRONT_RIGHT = 2;
+const int MOTOR_FRONT_LEFT = 3;
+
+void setupMotors() {
+	Serial.println("Setup Motors");
+
+	// configure pins
+	ledcAttach(MOTOR_0_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
+	ledcAttach(MOTOR_1_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
+	ledcAttach(MOTOR_2_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
+	ledcAttach(MOTOR_3_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
+
+	sendMotors();
+	Serial.println("Motors initialized");
+}
+
+int getDutyCycle(float value) {
+	value = constrain(value, 0, 1);
+	float duty = mapff(value, 0, 1, 0, (1 << PWM_RESOLUTION) - 1);
+	return round(duty);
+}
+
+void sendMotors() {
+	ledcWrite(MOTOR_0_PIN, getDutyCycle(motors[0]));
+	ledcWrite(MOTOR_1_PIN, getDutyCycle(motors[1]));
+	ledcWrite(MOTOR_2_PIN, getDutyCycle(motors[2]));
+	ledcWrite(MOTOR_3_PIN, getDutyCycle(motors[3]));
+}
+
+bool motorsActive() {
+	return motors[0] != 0 || motors[1] != 0 || motors[2] != 0 || motors[3] != 0;
+}
+
+void testMotor(int n) {
+	Serial.printf("Testing motor %d\n", n);
+	motors[n] = 1;
+	delay(50); // ESP32 may need to wait until the end of the current cycle to change duty https://github.com/espressif/arduino-esp32/issues/5306
+	sendMotors();
+	delay(3000);
+	motors[n] = 0;
+	sendMotors();
+	Serial.printf("Done\n");
+}

flix/pid.h

@@ -0,0 +1,48 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// PID controller implementation
+
+#pragma once
+
+#include "lpf.h"
+
+class PID {
+public:
+	float p = 0;
+	float i = 0;
+	float d = 0;
+	float windup = 0;
+
+	float derivative = 0;
+	float integral = 0;
+
+	LowPassFilter<float> lpf; // low pass filter for derivative term
+
+	PID(float p, float i, float d, float windup = 0, float dAlpha = 1) : p(p), i(i), d(d), windup(windup), lpf(dAlpha) {};
+
+	float update(float error, float dt) {
+		integral += error * dt;
+
+		if (isfinite(prevError) && dt > 0) {
+			// calculate derivative if both dt and prevError are valid
+			derivative = (error - prevError) / dt;
+
+			// apply low pass filter to derivative
+			derivative = lpf.update(derivative);
+		}
+
+		prevError = error;
+
+		return p * error + constrain(i * integral, -windup, windup) + d * derivative; // PID
+	}
+
+	void reset() {
+		prevError = NAN;
+		integral = 0;
+		derivative = 0;
+	}
+
+private:
+	float prevError = NAN;
+};

flix/quaternion.h

@@ -0,0 +1,212 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Lightweight rotation quaternion library
+
+#pragma once
+
+#include "vector.h"
+
+class Quaternion : public Printable {
+public:
+	float w, x, y, z;
+
+	Quaternion(): w(1), x(0), y(0), z(0) {};
+
+	Quaternion(float w, float x, float y, float z): w(w), x(x), y(y), z(z) {};
+
+	static Quaternion fromAxisAngle(const Vector& axis, float angle) {
+		float halfAngle = angle * 0.5;
+		float sin2 = sin(halfAngle);
+		float cos2 = cos(halfAngle);
+		float sinNorm = sin2 / axis.norm();
+		return Quaternion(cos2, axis.x * sinNorm, axis.y * sinNorm, axis.z * sinNorm);
+	}
+
+	static Quaternion fromRotationVector(const Vector& rotation) {
+		if (rotation.zero()) {
+			return Quaternion();
+		}
+		return Quaternion::fromAxisAngle(rotation, rotation.norm());
+	}
+
+	static Quaternion fromEuler(const Vector& euler) {
+		float cx = cos(euler.x / 2);
+		float cy = cos(euler.y / 2);
+		float cz = cos(euler.z / 2);
+		float sx = sin(euler.x / 2);
+		float sy = sin(euler.y / 2);
+		float sz = sin(euler.z / 2);
+
+		return Quaternion(
+			cx * cy * cz + sx * sy * sz,
+			sx * cy * cz - cx * sy * sz,
+			cx * sy * cz + sx * cy * sz,
+			cx * cy * sz - sx * sy * cz);
+	}
+
+	static Quaternion fromBetweenVectors(Vector u, Vector v) {
+		float dot = u.x * v.x + u.y * v.y + u.z * v.z;
+		float w1 = u.y * v.z - u.z * v.y;
+		float w2 = u.z * v.x - u.x * v.z;
+		float w3 = u.x * v.y - u.y * v.x;
+
+		Quaternion ret(
+			dot + sqrt(dot * dot + w1 * w1 + w2 * w2 + w3 * w3),
+			w1,
+			w2,
+			w3);
+		ret.normalize();
+		return ret;
+	}
+
+	bool finite() const {
+		return isfinite(w) && isfinite(x) && isfinite(y) && isfinite(z);
+	}
+
+	float norm() const {
+		return sqrt(w * w + x * x + y * y + z * z);
+	}
+
+	void normalize() {
+		float n = norm();
+		w /= n;
+		x /= n;
+		y /= n;
+		z /= n;
+	}
+
+	void toAxisAngle(Vector& axis, float& angle) const {
+		angle = acos(w) * 2;
+		axis.x = x / sin(angle / 2);
+		axis.y = y / sin(angle / 2);
+		axis.z = z / sin(angle / 2);
+	}
+
+	Vector toRotationVector() const {
+		if (w == 1 && x == 0 && y == 0 && z == 0) return Vector(0, 0, 0); // neutral quaternion
+		float angle;
+		Vector axis;
+		toAxisAngle(axis, angle);
+		return angle * axis;
+	}
+
+	Vector toEuler() const {
+		// https://github.com/ros/geometry2/blob/589caf083cae9d8fae7effdb910454b4681b9ec1/tf2/include/tf2/impl/utils.h#L87
+		Vector euler;
+		float sqx = x * x;
+		float sqy = y * y;
+		float sqz = z * z;
+		float sqw = w * w;
+		// Cases derived from https://orbitalstation.wordpress.com/tag/quaternion/
+		float sarg = -2 * (x * z - w * y) / (sqx + sqy + sqz + sqw);
+		if (sarg <= -0.99999) {
+			euler.x = 0;
+			euler.y = -0.5 * PI;
+			euler.z = -2 * atan2(y, x);
+		} else if (sarg >= 0.99999) {
+			euler.x = 0;
+			euler.y = 0.5 * PI;
+			euler.z = 2 * atan2(y, x);
+		} else {
+			euler.x = atan2(2 * (y * z + w * x), sqw - sqx - sqy + sqz);
+			euler.y = asin(sarg);
+			euler.z = atan2(2 * (x * y + w * z), sqw + sqx - sqy - sqz);
+		}
+		return euler;
+	}
+
+	float getYaw() const {
+		// https://github.com/ros/geometry2/blob/589caf083cae9d8fae7effdb910454b4681b9ec1/tf2/include/tf2/impl/utils.h#L122
+		float yaw;
+		float sqx = x * x;
+		float sqy = y * y;
+		float sqz = z * z;
+		float sqw = w * w;
+		double sarg = -2 * (x * z - w * y) / (sqx + sqy + sqz + sqw);
+		if (sarg <= -0.99999) {
+			yaw = -2 * atan2(y, x);
+		} else if (sarg >= 0.99999) {
+			yaw = 2 * atan2(y, x);
+		} else {
+			yaw = atan2(2 * (x * y + w * z), sqw + sqx - sqy - sqz);
+		}
+		return yaw;
+	}
+
+	void setYaw(float yaw) {
+		// TODO: optimize?
+		Vector euler = toEuler();
+		euler.z = yaw;
+		(*this) = Quaternion::fromEuler(euler);
+	}
+
+	Quaternion operator * (const Quaternion& q) const {
+		return Quaternion(
+			w * q.w - x * q.x - y * q.y - z * q.z,
+			w * q.x + x * q.w + y * q.z - z * q.y,
+			w * q.y + y * q.w + z * q.x - x * q.z,
+			w * q.z + z * q.w + x * q.y - y * q.x);
+	}
+
+	bool operator == (const Quaternion& q) const {
+		return w == q.w && x == q.x && y == q.y && z == q.z;
+	}
+
+	bool operator != (const Quaternion& q) const {
+		return !(*this == q);
+	}
+
+	Quaternion inversed() const {
+		float normSqInv = 1 / (w * w + x * x + y * y + z * z);
+		return Quaternion(
+			w * normSqInv,
+			-x * normSqInv,
+			-y * normSqInv,
+			-z * normSqInv);
+	}
+
+	Vector conjugate(const Vector& v) const {
+		Quaternion qv(0, v.x, v.y, v.z);
+		Quaternion res = (*this) * qv * inversed();
+		return Vector(res.x, res.y, res.z);
+	}
+
+	Vector conjugateInversed(const Vector& v) const {
+		Quaternion qv(0, v.x, v.y, v.z);
+		Quaternion res = inversed() * qv * (*this);
+		return Vector(res.x, res.y, res.z);
+	}
+
+	// Rotate quaternion by quaternion
+	static Quaternion rotate(const Quaternion& a, const Quaternion& b, const bool normalize = true) {
+		Quaternion rotated = a * b;
+		if (normalize) {
+			rotated.normalize();
+		}
+		return rotated;
+	}
+
+	// Rotate vector by quaternion
+	static Vector rotateVector(const Vector& v, const Quaternion& q) {
+		return q.conjugateInversed(v);
+	}
+
+	// Quaternion between two quaternions a and b
+	static Quaternion between(const Quaternion& a, const Quaternion& b, const bool normalize = true) {
+		Quaternion q = a * b.inversed();
+		if (normalize) {
+			q.normalize();
+		}
+		return q;
+	}
+
+	size_t printTo(Print& p) const {
+		size_t r = 0;
+		r += p.print(w, 15) + p.print(" ");
+		r += p.print(x, 15) + p.print(" ");
+		r += p.print(y, 15) + p.print(" ");
+		r += p.print(z, 15);
+		return r;
+	}
+};

flix/rc.ino

@@ -0,0 +1,80 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Work with the RC receiver
+
+#include <SBUS.h>
+#include "util.h"
+
+SBUS RC(Serial2); // NOTE: Use RC(Serial2, 16, 17) if you use the old UART2 pins
+
+uint16_t channels[16]; // raw rc channels
+float controlTime; // time of the last controls update
+
+
+// NOTE: use 'cr' command to calibrate the RC and put the values here
+int channelZero[] = {992, 992, 172, 992, 172, 172, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+int channelMax[] = {1811, 1811, 1811, 1811, 1811, 1811, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+
+// Channels mapping:
+int rollChannel = 0;
+int pitchChannel = 1;
+int throttleChannel = 2;
+int yawChannel = 3;
+int armedChannel = 4;
+int modeChannel = 5;
+
+void setupRC() {
+	Serial.println("Setup RC");
+	RC.begin();
+}
+
+bool readRC() {
+	if (RC.read()) {
+		SBUSData data = RC.data();
+		for (int i = 0; i < 16; i++) channels[i] = data.ch[i]; // copy channels data
+		normalizeRC();
+		controlTime = t;
+		return true;
+	}
+	return false;
+}
+
+void normalizeRC() {
+	float controls[16];
+	for (int i = 0; i < 16; i++) {
+		controls[i] = mapf(channels[i], channelZero[i], channelMax[i], 0, 1);
+	}
+	// Update control values
+	controlRoll = controls[rollChannel];
+	controlPitch = controls[pitchChannel];
+	controlYaw = controls[yawChannel];
+	controlThrottle = controls[throttleChannel];
+	controlArmed = controls[armedChannel];
+	controlMode = controls[modeChannel];
+}
+
+void calibrateRC() {
+	Serial.println("Calibrate RC: move all sticks to maximum positions [4 sec]");
+	Serial.println("··o     ··o\n···     ···\n···     ···");
+	delay(4000);
+	while (!readRC());
+	for (int i = 0; i < 16; i++) {
+		channelMax[i] = channels[i];
+	}
+	Serial.println("Calibrate RC: move all sticks to neutral positions [4 sec]");
+	Serial.println("···     ···\n···     ·o·\n·o·     ···");
+	delay(4000);
+	while (!readRC());
+	for (int i = 0; i < 16; i++) {
+		channelZero[i] = channels[i];
+	}
+	printRCCalibration();
+}
+
+void printRCCalibration() {
+	for (int i = 0; i < sizeof(channelZero) / sizeof(channelZero[0]); i++) Serial.printf("%d ", channelZero[i]);
+	Serial.printf("\n");
+	for (int i = 0; i < sizeof(channelMax) / sizeof(channelMax[0]); i++) Serial.printf("%d ", channelMax[i]);
+	Serial.printf("\n");
+}

flix/time.ino

@@ -0,0 +1,29 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Time related functions
+
+float loopRate; // Hz
+
+void step() {
+	float now = micros() / 1000000.0;
+	dt = now - t;
+	t = now;
+
+	if (!(dt > 0)) {
+		dt = 0; // assume dt to be zero on first step and on reset
+	}
+
+	computeLoopRate();
+}
+
+void computeLoopRate() {
+	static float windowStart = 0;
+	static uint32_t rate = 0;
+	rate++;
+	if (t - windowStart >= 1) { // 1 second window
+		loopRate = rate;
+		windowStart = t;
+		rate = 0;
+	}
+}

flix/util.h

@@ -0,0 +1,36 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Utility functions
+
+#pragma once
+
+#include <math.h>
+#include <soc/soc.h>
+#include <soc/rtc_cntl_reg.h>
+
+const float ONE_G = 9.80665;
+
+float mapf(long x, long in_min, long in_max, float out_min, float out_max) {
+	return (float)(x - in_min) * (out_max - out_min) / (float)(in_max - in_min) + out_min;
+}
+
+float mapff(float x, float in_min, float in_max, float out_min, float out_max) {
+	return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+}
+
+// Wrap angle to [-PI, PI)
+float wrapAngle(float angle) {
+	angle = fmodf(angle, 2 * PI);
+	if (angle > PI) {
+		angle -= 2 * PI;
+	} else if (angle < -PI) {
+		angle += 2 * PI;
+	}
+	return angle;
+}
+
+// Disable reset on low voltage
+void disableBrownOut() {
+	REG_CLR_BIT(RTC_CNTL_BROWN_OUT_REG, RTC_CNTL_BROWN_OUT_ENA);
+}

flix/vector.h

@@ -0,0 +1,113 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Lightweight vector library
+
+#pragma once
+
+class Vector : public Printable {
+public:
+	float x, y, z;
+
+	Vector(): x(0), y(0), z(0) {};
+
+	Vector(float x, float y, float z): x(x), y(y), z(z) {};
+
+	bool zero() const {
+		return x == 0 && y == 0 && z == 0;
+	}
+
+	bool finite() const {
+		return isfinite(x) && isfinite(y) && isfinite(z);
+	}
+
+	float norm() const {
+		return sqrt(x * x + y * y + z * z);
+	}
+
+	void normalize() {
+		float n = norm();
+		x /= n;
+		y /= n;
+		z /= n;
+	}
+
+	Vector operator + (const float b) const {
+		return Vector(x + b, y + b, z + b);
+	}
+
+	Vector operator * (const float b) const {
+		return Vector(x * b, y * b, z * b);
+	}
+
+	Vector operator / (const float b) const {
+		return Vector(x / b, y / b, z / b);
+	}
+
+	Vector operator + (const Vector& b) const {
+		return Vector(x + b.x, y + b.y, z + b.z);
+	}
+
+	Vector operator - (const Vector& b) const {
+		return Vector(x - b.x, y - b.y, z - b.z);
+	}
+
+	Vector& operator += (const Vector& b) {
+		return *this = *this + b;
+	}
+
+	Vector& operator -= (const Vector& b) {
+		return *this = *this - b;
+	}
+
+	// Element-wise multiplication
+	Vector operator * (const Vector& b) const {
+		return Vector(x * b.x, y * b.y, z * b.z);
+	}
+
+	// Element-wise division
+	Vector operator / (const Vector& b) const {
+		return Vector(x / b.x, y / b.y, z / b.z);
+	}
+
+	bool operator == (const Vector& b) const {
+		return x == b.x && y == b.y && z == b.z;
+	}
+
+	bool operator != (const Vector& b) const {
+		return !(*this == b);
+	}
+
+	static float dot(const Vector& a, const Vector& b) {
+		return a.x * b.x + a.y * b.y + a.z * b.z;
+	}
+
+	static Vector cross(const Vector& a, const Vector& b) {
+		return Vector(a.y * b.z - a.z * b.y, a.z * b.x - a.x * b.z, a.x * b.y - a.y * b.x);
+	}
+
+	static float angleBetween(const Vector& a, const Vector& b) {
+		return acos(constrain(dot(a, b) / (a.norm() * b.norm()), -1, 1));
+	}
+
+	static Vector rotationVectorBetween(const Vector& a, const Vector& b) {
+		Vector direction = cross(a, b);
+		if (direction.zero()) {
+			// vectors are opposite, return any perpendicular vector
+			return cross(a, Vector(1, 0, 0));
+		}
+		direction.normalize();
+		float angle = angleBetween(a, b);
+		return direction * angle;
+	}
+
+	size_t printTo(Print& p) const {
+		return
+			p.print(x, 15) + p.print(" ") +
+			p.print(y, 15) + p.print(" ") +
+			p.print(z, 15);
+	}
+};
+
+Vector operator * (const float a, const Vector& b) { return b * a; }
+Vector operator + (const float a, const Vector& b) { return b + a; }

flix/wifi.ino

@@ -0,0 +1,36 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Wi-Fi support
+
+#if WIFI_ENABLED
+
+#include <WiFi.h>
+#include <WiFiAP.h>
+#include <WiFiUdp.h>
+
+#define WIFI_SSID "flix"
+#define WIFI_PASSWORD "flixwifi"
+#define WIFI_UDP_PORT 14550
+#define WIFI_UDP_REMOTE_PORT 14550
+
+WiFiUDP udp;
+
+void setupWiFi() {
+	Serial.println("Setup Wi-Fi");
+	WiFi.softAP(WIFI_SSID, WIFI_PASSWORD);
+	udp.begin(WIFI_UDP_PORT);
+}
+
+void sendWiFi(const uint8_t *buf, int len) {
+	udp.beginPacket(WiFi.softAPBroadcastIP(), WIFI_UDP_REMOTE_PORT);
+	udp.write(buf, len);
+	udp.endPacket();
+}
+
+int receiveWiFi(uint8_t *buf, int len) {
+	udp.parsePacket();
+	return udp.read(buf, len);
+}
+
+#endif

gazebo/Arduino.h

@@ -0,0 +1,144 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Partial implementation of Arduino API for simulation
+
+#pragma once
+
+#include <cmath>
+#include <string>
+#include <stdint.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/poll.h>
+
+#define PI 3.1415926535897932384626433832795
+#define DEG_TO_RAD 0.017453292519943295769236907684886
+#define RAD_TO_DEG 57.295779513082320876798154814105
+#define radians(deg) ((deg)*DEG_TO_RAD)
+#define degrees(rad) ((rad)*RAD_TO_DEG)
+
+#define constrain(amt,low,high) ((amt)<(low)?(low):((amt)>(high)?(high):(amt)))
+
+long map(long x, long in_min, long in_max, long out_min, long out_max) {
+	const long run = in_max - in_min;
+	const long rise = out_max - out_min;
+	const long delta = x - in_min;
+	return (delta * rise) / run + out_min;
+}
+
+class __FlashStringHelper;
+
+// Arduino String partial implementation
+// https://www.arduino.cc/reference/en/language/variables/data-types/stringobject/
+class String: public std::string {
+public:
+	long toInt() const { return atol(this->c_str()); }
+	float toFloat() const { return atof(this->c_str()); }
+	bool isEmpty() const { return this->empty(); }
+};
+
+class Print;
+
+class Printable {
+public:
+	virtual size_t printTo(Print& p) const = 0;
+};
+
+class Print {
+public:
+	size_t printf(const char *format, ...) {
+		va_list args;
+		va_start(args, format);
+		size_t result = vprintf(format, args);
+		va_end(args);
+		return result;
+	}
+
+	size_t print(int n) {
+		return printf("%d", n);
+	}
+
+	size_t print(float n, int digits = 2) {
+		return printf("%.*f", digits, n);
+	}
+
+	size_t println(float n, int digits = 2) {
+		return printf("%.*f\n", digits, n);
+	}
+
+	size_t print(const char* s) {
+		return printf("%s", s);
+	}
+
+	size_t println() {
+		return print("\n");
+	}
+
+	size_t println(const char* s) {
+		return printf("%s\n", s);
+	}
+
+	size_t println(const Printable& p) {
+		return p.printTo(*this) + print("\n");
+	}
+
+	size_t print(const String& s) {
+		return printf("%s", s.c_str());
+	}
+
+	size_t println(const std::string& s) {
+		return printf("%s\n", s.c_str());
+	}
+
+	size_t println(const String& s) {
+		return printf("%s\n", s.c_str());
+	}
+};
+
+class HardwareSerial: public Print {
+public:
+	void begin(unsigned long baud) {
+		// server is running in background by default, so it doesn't have access to stdin
+		// https://github.com/gazebosim/gazebo-classic/blob/d45feeb51f773e63960616880b0544770b8d1ad7/gazebo/gazebo_main.cc#L216
+		// set foreground process group to current process group to allow reading from stdin
+		// https://stackoverflow.com/questions/58918188/why-is-stdin-not-propagated-to-child-process-of-different-process-group
+		signal(SIGTTOU, SIG_IGN);
+		tcsetpgrp(STDIN_FILENO, getpgrp());
+		signal(SIGTTOU, SIG_DFL);
+	};
+
+	int available() {
+		// to implement for Windows, see https://stackoverflow.com/a/71992965/6850197
+		struct pollfd pfd = { .fd = STDIN_FILENO, .events = POLLIN };
+		return poll(&pfd, 1, 0) > 0;
+	}
+
+	int read() {
+		if (available()) {
+			char c;
+			size_t res = ::read(STDIN_FILENO, &c, 1); // use raw read to avoid C++ buffering
+			// https://stackoverflow.com/questions/45238997/does-getchar-function-has-its-own-buffer-to-store-remaining-input
+			return c;
+		}
+		return -1;
+	}
+
+	void setRxInvert(bool invert) {};
+};
+
+HardwareSerial Serial, Serial2;
+
+void delay(uint32_t ms) {
+	std::this_thread::sleep_for(std::chrono::milliseconds(ms));
+}
+
+bool ledcAttach(uint8_t pin, uint32_t freq, uint8_t resolution) { return true; }
+bool ledcWrite(uint8_t pin, uint32_t duty) { return true; }
+
+unsigned long __micros;
+unsigned long __resetTime = 0;
+
+unsigned long micros() {
+	return __micros + __resetTime; // keep the time monotonic
+}

gazebo/CMakeLists.txt

@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.5 FATAL_ERROR)
+project(flix_gazebo)
+
+# === gazebo plugin
+find_package(gazebo REQUIRED)
+find_package(SDL2 REQUIRED)
+include_directories(${GAZEBO_INCLUDE_DIRS})
+link_directories(${GAZEBO_LIBRARY_DIRS})
+list(APPEND CMAKE_CXX_FLAGS "${GAZEBO_CXX_FLAGS}")
+
+set(FLIX_SOURCE_DIR ../flix)
+include_directories(${FLIX_SOURCE_DIR})
+
+set(CMAKE_BUILD_TYPE RelWithDebInfo)
+add_library(flix SHARED simulator.cpp)
+target_link_libraries(flix ${GAZEBO_LIBRARIES} ${SDL2_LIBRARIES})
+target_include_directories(flix PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+target_compile_options(flix PRIVATE -Wno-address-of-packed-member) # disable unneeded mavlink warnings
+
+# Include dir for MAVLink-Arduino library
+target_include_directories(flix PUBLIC $ENV{HOME}/Arduino/libraries/MAVLink)
+target_include_directories(flix PUBLIC $ENV{HOME}/Documents/Arduino/libraries/MAVLink)

gazebo/README.md

@@ -0,0 +1,15 @@
+# Gazebo Simulation
+
+<img src="../docs/img/simulator.png" width=500 alt="Flix simulator">
+
+## Building and running
+
+See [building and running instructions](../docs/build.md#simulation).
+
+## Code structure
+
+Flix simulator is based on [Gazebo Classic](https://classic.gazebosim.org) and consists of the following components:
+
+* Physical model of the drone: [`models/flix/flix.sdf`](models/flix/flix.sdf).
+* Plugin for Gazebo: [`simulator.cpp`](simulator.cpp). The plugin is attached to the physical model. It receives stick positions from the controller, gets the data from the virtual sensors, and then passes this data to the Arduino code.
+* Arduino imitation: [`Arduino.h`](Arduino.h). This file contains partial implementation of the Arduino API, that is working within Gazebo plugin environment.

gazebo/SBUS.h

@@ -0,0 +1,26 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// SBUS library mock to make it possible to compile simulator with rc.ino
+
+#include "joystick.h"
+
+struct SBUSData {
+	int16_t ch[16];
+};
+
+class SBUS {
+public:
+	SBUS(HardwareSerial& bus, const bool inv = true) {};
+	SBUS(HardwareSerial& bus, const int8_t rxpin, const int8_t txpin, const bool inv = true) {};
+	void begin() {};
+	bool read() { return joystickInit(); };
+	SBUSData data() {
+		SBUSData data;
+		joystickGet(data.ch);
+		for (int i = 0; i < 16; i++) {
+			data.ch[i] = map(data.ch[i], -32768, 32767, 1000, 2000); // convert to pulse width style
+		}
+		return data;
+	};
+};

gazebo/flix.h

@@ -0,0 +1,53 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Declarations of some functions and variables in Arduino code
+
+#include <cmath>
+#include <stdio.h>
+#include "vector.h"
+#include "quaternion.h"
+#include "Arduino.h"
+#include "wifi.h"
+
+#define WIFI_ENABLED 1
+
+float t = NAN;
+float dt;
+float motors[4];
+float controlRoll, controlPitch, controlYaw, controlThrottle, controlArmed, controlMode;
+Vector acc;
+Vector gyro;
+Vector rates;
+Quaternion attitude;
+
+// declarations
+void computeLoopRate();
+void applyGyro();
+void applyAcc();
+void control();
+void interpretRC();
+void controlAttitude();
+void controlRate();
+void controlTorque();
+void showTable();
+void sendMotors();
+bool motorsActive();
+void doCommand(const String& command);
+void normalizeRC();
+void printRCCalibration();
+void processMavlink();
+void sendMavlink();
+void sendMessage(const void *msg);
+void receiveMavlink();
+void handleMavlink(const void *_msg);
+void failsafe();
+void descend();
+inline Quaternion fluToFrd(const Quaternion &q);
+
+// mocks
+void setLED(bool on) {};
+void calibrateGyro() { printf("Skip gyro calibrating\n"); };
+void calibrateAccel() { printf("Skip accel calibrating\n"); };
+void printIMUCalibration() { printf("cal: N/A\n"); };
+void printIMUInfo() {};

gazebo/flix.world

@@ -0,0 +1,29 @@
+<?xml version="1.0"?>
+<sdf version="1.4">
+	<world name="default">
+		<scene>
+			<ambient>1 1 1 1</ambient>
+			<sky/>
+			<origin_visual>false</origin_visual>
+			<grid>false</grid>
+		</scene>
+		<gui>
+			<camera name="user_camera">
+				<pose>-2.3 0 1.1 0 0.3 0</pose>
+			</camera>
+		</gui>
+		<physics type="ode">
+			<max_step_size>0.001</max_step_size>
+		</physics>
+		<include>
+			<uri>model://floor</uri>
+		</include>
+		<include>
+			<uri>model://sun</uri>
+		</include>
+		<include>
+			<uri>model://flix</uri>
+			<pose>0 0 0.3 0 0 0</pose>
+		</include>
+	</world>
+</sdf>

gazebo/joystick.h

@@ -0,0 +1,65 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Joystick support for simulation
+
+#include <SDL2/SDL.h>
+#include <gazebo/gazebo.hh>
+#include <iostream>
+
+// simulation calibration overrides, NOTE: use `cr` command and replace with the actual values
+const int channelZeroOverride[] = {1500, 0, 1000, 1500, 1500, 1000};
+const int channelMaxOverride[] = {2000, 2000, 2000, 2000, 2000, 2000};
+
+// channels mapping overrides
+const int rollChannelOverride = 3;
+const int pitchChannelOverride = 4;
+const int throttleChannelOverride = 5;
+const int yawChannelOverride = 0;
+const int armedChannelOverride = 2;
+const int modeChannelOverride = 1;
+
+SDL_Joystick *joystick;
+
+void normalizeRC();
+
+bool joystickInit() {
+	static bool joystickInitialized = false;
+	static bool warnShown = false;
+	if (joystickInitialized) return true;
+
+	SDL_Init(SDL_INIT_JOYSTICK);
+	joystick = SDL_JoystickOpen(0);
+	if (joystick != NULL) {
+		joystickInitialized = true;
+		gzmsg << "Joystick initialized: " << SDL_JoystickNameForIndex(0) << std::endl;
+	} else if (!warnShown) {
+		gzwarn << "Joystick not found, begin waiting for joystick..." << std::endl;
+		warnShown = true;
+	}
+
+	// apply overrides
+	extern int channelZero[16];
+	extern int channelMax[16];
+	memcpy(channelZero, channelZeroOverride, sizeof(channelZeroOverride));
+	memcpy(channelMax, channelMaxOverride, sizeof(channelMaxOverride));
+
+	extern int rollChannel, pitchChannel, throttleChannel, yawChannel, armedChannel, modeChannel;
+	rollChannel = rollChannelOverride;
+	pitchChannel = pitchChannelOverride;
+	throttleChannel = throttleChannelOverride;
+	yawChannel = yawChannelOverride;
+	armedChannel = armedChannelOverride;
+	modeChannel = modeChannelOverride;
+
+	return joystickInitialized;
+}
+
+bool joystickGet(int16_t ch[16]) {
+	SDL_JoystickUpdate();
+
+	for (uint8_t i = 0; i < 16; i++) {
+		ch[i] = SDL_JoystickGetAxis(joystick, i);
+	}
+	return true;
+}

gazebo/models/flix/flix.sdf

@@ -0,0 +1,71 @@
+<?xml version="1.0"?>
+<sdf version="1.5">
+	<model name="flix">
+		<plugin name="flix" filename="libflix.so"/>
+		<link name="body">
+			<inertial>
+				<mass>0.065</mass>
+				<inertia>
+					<ixx>3.55E-5</ixx>
+					<iyy>4.23E-5</iyy>
+					<izz>7.47E-5</izz>
+				</inertia>
+			</inertial>
+			<collision name="collision">
+				<geometry>
+					<box>
+						<size>0.095 0.095 0.0276</size>
+					</box>
+				</geometry>
+			</collision>
+			<sensor name="imu" type="imu">
+				<always_on>1</always_on>
+				<visualize>1</visualize>
+				<update_rate>1000</update_rate>
+				<imu>
+					<angular_velocity>
+						<x><noise type="gaussian"><stddev>0.00174533</stddev></noise></x><!-- 0.1 degrees per second -->
+						<y><noise type="gaussian"><stddev>0.00174533</stddev></noise></y>
+						<z><noise type="gaussian"><stddev>0.00174533</stddev></noise></z>
+					</angular_velocity>
+					<linear_acceleration>
+						<x><noise type="gaussian"><stddev>0.0784</stddev></noise></x><!-- 8 mg -->
+						<y><noise type="gaussian"><stddev>0.0784</stddev></noise></y>
+						<z><noise type="gaussian"><stddev>0.0784</stddev></noise></z>
+					</linear_acceleration>
+				</imu>
+			</sensor>
+			<visual name="body">
+				<geometry>
+					<mesh><uri>model://flix/flix.stl</uri></mesh>
+				</geometry>
+				<material>
+					<ambient>0.5 0.5 0.6 1</ambient>
+					<diffuse>0.5 0.5 0.6 1</diffuse>
+					<specular>0 0 0 1</specular>
+					<emissive>0 0 0 1</emissive>
+				</material>
+			</visual>
+			<visual name="prop0"><!-- rear left -->
+				<geometry><cylinder><radius>0.0275</radius><length>0</length></cylinder></geometry>
+				<pose>-0.04243 0.04243 0.0142 0 0 0</pose>
+				<material><ambient>0.8 0.3 0.3 0.5</ambient><diffuse>0.8 0.3 0.3 0.5</diffuse></material>
+			</visual>
+			<visual name="prop1"><!-- rear right -->
+				<geometry><cylinder><radius>0.0275</radius><length>0</length></cylinder></geometry>
+				<pose>-0.04243 -0.04243 0.0142 0 0 0</pose>
+				<material><ambient>0.8 0.3 0.3 0.5</ambient><diffuse>0.8 0.3 0.3 0.5</diffuse></material>
+			</visual>
+			<visual name="prop2"><!-- front right -->
+				<geometry><cylinder><radius>0.0275</radius><length>0</length></cylinder></geometry>
+				<pose>0.04243 -0.04243 0.0142 0 0 0</pose>
+				<material><ambient>1 1 1 0.5</ambient><diffuse>1 1 1 0.5</diffuse></material>
+			</visual>
+			<visual name="prop3"><!-- front left -->
+				<geometry><cylinder><radius>0.0275</radius><length>0</length></cylinder></geometry>
+				<pose>0.04243 0.04243 0.0142 0 0 0</pose>
+				<material><ambient>1 1 1 0.5</ambient><diffuse>1 1 1 0.5</diffuse></material>
+			</visual>
+		</link>
+	</model>
+</sdf>

gazebo/models/flix/model.config

@@ -0,0 +1,14 @@
+<?xml version="1.0"?>
+<model>
+    <name>flix</name>
+    <version>1.0</version>
+    <sdf version="1.5">flix.sdf</sdf>
+    <author>
+        <name>Oleg Kalachev</name>
+        <email>okalachev@gmail.com</email>
+    </author>
+    <license>Unknown</license>
+    <description>
+        Flix quadrotor
+    </description>
+</model>

gazebo/models/floor/floor.sdf

@@ -0,0 +1,31 @@
+<?xml version="1.0"?>
+<sdf version="1.5">
+	<model name="floor">
+		<static>true</static>
+		<link name="link">
+			<pose>0 0 -0.02 0 0 0</pose>
+			<collision name="collision">
+				<geometry>
+					<box>
+						<size>200 200 .02</size>
+					</box>
+				</geometry>
+			</collision>
+			<visual name="visual">
+				<cast_shadows>false</cast_shadows>
+				<geometry>
+					<box>
+						<size>200 200 .02</size>
+					</box>
+				</geometry>
+				<material>
+					<script>
+						<uri>model://floor/materials/scripts</uri>
+						<uri>model://floor/materials/textures</uri>
+						<name>parquet</name>
+					</script>
+				</material>
+			</visual>
+		</link>
+	</model>
+</sdf>

gazebo/models/floor/materials/scripts/floor.material

@@ -0,0 +1,20 @@
+material parquet
+{
+	technique
+	{
+		pass
+		{
+			ambient 0.5 0.5 0.5 1.0
+			diffuse 0.5 0.5 0.5 1.0
+			specular 0.2 0.2 0.2 1.0 12.5
+
+			texture_unit
+			{
+				texture floor.jpg
+				filtering anistropic
+				max_anisotropy 16
+				scale 0.01 0.01
+			}
+		}
+	}
+}

gazebo/models/floor/model.config

@@ -0,0 +1,19 @@
+<?xml version="1.0"?>
+
+<model>
+  <name>Floor</name>
+  <version>1.0</version>
+  <sdf version="1.5">floor.sdf</sdf>
+
+  <author>
+    <name>Oleg Kalachev</name>
+    <email>okalachev@gmail.com</email>
+  </author>
+
+  <license>Unknown</license>
+
+  <description>
+    Floor.
+  </description>
+
+</model>

gazebo/models/linnmon/linnmon.sdf

@@ -0,0 +1,23 @@
+<?xml version="1.0"?>
+<sdf version="1.5">
+	<model name="table1">
+		<static>true</static>
+		<link name="link">
+			<pose>0 0 0 0 0 0</pose>
+			<collision name="mesh">
+				<geometry>
+					<mesh>
+						<uri>model://linnmon/linnmon.dae</uri>
+					</mesh>
+				</geometry>
+			</collision>
+			<visual name="visual">
+				<geometry>
+					<mesh>
+						<uri>model://linnmon/linnmon.dae</uri>
+					</mesh>
+				</geometry>
+			</visual>
+		</link>
+	</model>
+</sdf>

gazebo/models/linnmon/model.config

@@ -0,0 +1,19 @@
+<?xml version="1.0"?>
+
+<model>
+  <name>linnmon</name>
+  <version>1.0</version>
+  <sdf version="1.5">linnmon.sdf</sdf>
+
+  <author>
+    <name>Oleg Kalachev</name>
+    <email>okalachev@gmail.com</email>
+  </author>
+
+  <license>Unknown</license>
+
+  <description>
+    Linnmon table from https://3dlancer.net/en/producermodels/tables-coffee-tables/3dmodel-table-with-ikea-linnmon-36059
+  </description>
+
+</model>

gazebo/simulator.cpp

@@ -0,0 +1,134 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Gazebo plugin for running Arduino code and simulating the drone
+
+#include <functional>
+#include <cmath>
+#include <gazebo/gazebo.hh>
+#include <gazebo/physics/physics.hh>
+#include <gazebo/common/common.hh>
+#include <gazebo/sensors/sensors.hh>
+#include <gazebo/msgs/msgs.hh>
+#include <ignition/math/Vector3.hh>
+#include <ignition/math/Pose3.hh>
+#include <iostream>
+#include <fstream>
+
+#include "Arduino.h"
+#include "flix.h"
+#include "rc.ino"
+#include "time.ino"
+#include "motors.ino"
+#include "estimate.ino"
+#include "control.ino"
+#include "log.ino"
+#include "cli.ino"
+#include "mavlink.ino"
+#include "failsafe.ino"
+#include "lpf.h"
+
+using ignition::math::Vector3d;
+using namespace gazebo;
+using namespace std;
+
+class ModelFlix : public ModelPlugin {
+private:
+	physics::ModelPtr model;
+	physics::LinkPtr body;
+	sensors::ImuSensorPtr imu;
+	event::ConnectionPtr updateConnection, resetConnection;
+	transport::NodePtr nodeHandle;
+	transport::PublisherPtr motorPub[4];
+	LowPassFilter<Vector> accFilter = LowPassFilter<Vector>(0.1);
+
+public:
+	void Load(physics::ModelPtr _parent, sdf::ElementPtr /*_sdf*/) {
+		this->model = _parent;
+		this->body = this->model->GetLink("body");
+		this->imu = dynamic_pointer_cast<sensors::ImuSensor>(sensors::get_sensor(model->GetScopedName(true) + "::body::imu")); // default::flix::body::imu
+		this->updateConnection = event::Events::ConnectWorldUpdateBegin(std::bind(&ModelFlix::OnUpdate, this));
+		this->resetConnection = event::Events::ConnectWorldReset(std::bind(&ModelFlix::OnReset, this));
+		initNode();
+		Serial.begin(0);
+		gzmsg << "Flix plugin loaded" << endl;
+	}
+
+	void OnReset() {
+		attitude = Quaternion(); // reset estimated attitude
+		__resetTime += __micros;
+		gzmsg << "Flix plugin reset" << endl;
+	}
+
+	void OnUpdate() {
+		__micros = model->GetWorld()->SimTime().Double() * 1000000;
+		step();
+
+		// read virtual imu
+		gyro = Vector(imu->AngularVelocity().X(), imu->AngularVelocity().Y(), imu->AngularVelocity().Z());
+		acc = this->accFilter.update(Vector(imu->LinearAcceleration().X(), imu->LinearAcceleration().Y(), imu->LinearAcceleration().Z()));
+
+		// read rc
+		readRC();
+		controlMode = 1; // 0 acro, 1 stab
+		controlArmed = 1; // armed
+
+		estimate();
+
+		// correct yaw to the actual yaw
+		attitude.setYaw(this->model->WorldPose().Yaw());
+
+		control();
+		handleInput();
+		processMavlink();
+
+		applyMotorForces();
+		publishTopics();
+		logData();
+	}
+
+	void applyMotorForces() {
+		// thrusts
+		const double dist = 0.035355; // motors shift from the center, m
+		const double maxThrust = 0.03 * ONE_G; // ~30 g, https://youtu.be/VtKI4Pjx8Sk?&t=78
+
+		const float scale0 = 1.0, scale1 = 1.1, scale2 = 0.9, scale3 = 1.05; // imitating motors asymmetry
+		float mfl = scale0 * maxThrust * motors[MOTOR_FRONT_LEFT];
+		float mfr = scale1 * maxThrust * motors[MOTOR_FRONT_RIGHT];
+		float mrl = scale2 * maxThrust * motors[MOTOR_REAR_LEFT];
+		float mrr = scale3 * maxThrust * motors[MOTOR_REAR_RIGHT];
+
+		body->AddLinkForce(Vector3d(0.0, 0.0, mfl), Vector3d(dist, dist, 0.0));
+		body->AddLinkForce(Vector3d(0.0, 0.0, mfr), Vector3d(dist, -dist, 0.0));
+		body->AddLinkForce(Vector3d(0.0, 0.0, mrl), Vector3d(-dist, dist, 0.0));
+		body->AddLinkForce(Vector3d(0.0, 0.0, mrr), Vector3d(-dist, -dist, 0.0));
+
+		// torque
+		const double maxTorque = 0.0024 * ONE_G; // ~24 g*cm
+		body->AddRelativeTorque(Vector3d(0.0, 0.0, scale0 * maxTorque * motors[MOTOR_FRONT_LEFT]));
+		body->AddRelativeTorque(Vector3d(0.0, 0.0, scale1 * -maxTorque * motors[MOTOR_FRONT_RIGHT]));
+		body->AddRelativeTorque(Vector3d(0.0, 0.0, scale2 * -maxTorque * motors[MOTOR_REAR_LEFT]));
+		body->AddRelativeTorque(Vector3d(0.0, 0.0, scale3 * maxTorque * motors[MOTOR_REAR_RIGHT]));
+	}
+
+	void initNode() {
+		nodeHandle = transport::NodePtr(new transport::Node());
+		nodeHandle->Init();
+		string ns = "~/" + model->GetName();
+		// create motors output topics for debugging and plotting
+		motorPub[0] = nodeHandle->Advertise<msgs::Int>(ns + "/motor0");
+		motorPub[1] = nodeHandle->Advertise<msgs::Int>(ns + "/motor1");
+		motorPub[2] = nodeHandle->Advertise<msgs::Int>(ns + "/motor2");
+		motorPub[3] = nodeHandle->Advertise<msgs::Int>(ns + "/motor3");
+	}
+
+	void publishTopics() {
+		for (int i = 0; i < 4; i++) {
+			msgs::Int msg;
+			msg.set_data(static_cast<int>(round(motors[i] * 1000)));
+			motorPub[i]->Publish(msg);
+		}
+	}
+};
+
+GZ_REGISTER_MODEL_PLUGIN(ModelFlix)

gazebo/soc/rtc_cntl_reg.h

@@ -0,0 +1 @@
+// Dummy file to make it possible to compile simulator with Flix' util.h

gazebo/soc/soc.h

@@ -0,0 +1,4 @@
+// Dummy file to make it possible to compile simulator with Flix' util.h
+
+#define WRITE_PERI_REG(addr, val) {}
+#define REG_CLR_BIT(_r, _b) {}

gazebo/wifi.h

@@ -0,0 +1,44 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// sendWiFi and receiveWiFi implementations for the simulation
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#include <sys/poll.h>
+#include <gazebo/gazebo.hh>
+
+#define WIFI_UDP_PORT 14580
+#define WIFI_UDP_REMOTE_PORT 14550
+
+int wifiSocket;
+
+void setupWiFi() {
+	wifiSocket = socket(AF_INET, SOCK_DGRAM, 0);
+	sockaddr_in addr; // local address
+	addr.sin_family = AF_INET;
+	addr.sin_addr.s_addr = INADDR_ANY;
+	addr.sin_port = htons(WIFI_UDP_PORT);
+	bind(wifiSocket, (sockaddr *)&addr, sizeof(addr));
+	int broadcast = 1;
+	setsockopt(wifiSocket, SOL_SOCKET, SO_BROADCAST, &broadcast, sizeof(broadcast)); // enable broadcast
+	gzmsg << "WiFi UDP socket initialized on port " << WIFI_UDP_PORT << " (remote port " << WIFI_UDP_REMOTE_PORT << ")" << std::endl;
+}
+
+void sendWiFi(const uint8_t *buf, int len) {
+	if (wifiSocket == 0) setupWiFi();
+	sockaddr_in addr; // remote address
+	addr.sin_family = AF_INET;
+	addr.sin_addr.s_addr = INADDR_BROADCAST; // send UDP broadcast
+	addr.sin_port = htons(WIFI_UDP_REMOTE_PORT);
+	sendto(wifiSocket, buf, len, 0, (sockaddr *)&addr, sizeof(addr));
+}
+
+int receiveWiFi(uint8_t *buf, int len) {
+	struct pollfd pfd = { .fd = wifiSocket, .events = POLLIN };
+	if (poll(&pfd, 1, 0) <= 0) return 0; // check if there is data to read
+	return recv(wifiSocket, buf, len, 0);
+}

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